Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[christophernel via Polymer]

I would consider this to be a bug, or at the very least a design flaw. It's 
not readily apparent that you are defining prototypes in the property 
specifications. Shared state through parent prototypes seems to violate the 
whole nature of reusable components. I think property defaults should be 
mixed into the instantiated object, rather than shared across all instances.

On Thursday, January 4, 2018 at 6:17:59 AM UTC-8, Lars Knudsen wrote:
>
> I think this should rather be explained clearly in the guidelines. It is a 
> valuable thing when needed
>
> On Jan 4, 2018 07:57, > wrote:
>
>> Totally agree. Many developers won't know this after they finish reading 
>> the tutorial. It's like learning Python without being warned of the 
>> differences between class variables and instance variables.
>> To keep a shared state across multiple same type of elements, is not a 
>> daily demand, but will cause potential troubles in a daily work.
>>
>> On Wednesday, April 12, 2017 at 5:49:07 PM UTC+2, mpa...@ugcloud.ca 
>> wrote:
>>>
>>> I agree fully with Toni, Polymer is designed to help make web 
>>> components, and I thought the idea of a web component is that is isolated.  
>>> This make it easy to test and re-use etc.  If having multiple copies of an 
>>> element changes the behavior of it that would makes this harder to test and 
>>> not intuitive.  I can see people not testing multiple copies of their 
>>> elements, I have created 8 elements and it wasn't until my 9th one I 
>>> noticed this issue.  I now have to go back and double check everything.
>>>
>>> I would actually suggest removing the static array (object) option 
>>> completely, as you can simple use a parent object to handle this kind of 
>>> situation, and I think this would be the minority of cases anyway.
>>>
>>> On Sunday, October 23, 2016 at 3:59:14 PM UTC-4, Toni wrote:

 Although this question is a few months old, I ran into this problem 
 just now and was not able to solve it immediately with the explanation 
 given. So for anyone still having issues with this, here is the solution 
 (without telling you to go anywhere else and try to find it in the 
 documentation...):

 1. By default, properties of Polymer objects are shared across all 
 instances of the object (or, to be more precise, all references to the 
 object, since Polymer doesn't create new instances, as in "new 
 Element()"). 
 Basically, all properties are by default static. 
 2. Every property that is supposed to be individual to the specific 
 reference, in other words, be not static, and changable without messing 
 with any other instance/reference, has to have the field "value: 
 function() 
 { return []; }". 
 3. Example: 

 Polymer({
 is: 'txt-carousel-view',
 properties: {
 myOwnList: {
 value: function() { return []; } // this is a non-static 
 array, invididual and fresh for every instance 
 },
 mySharedList: {
 value: []; // this is a static array, shared with every 
 instance array
 }
 }
 })
  
 As a Polymer newbie, I assumed that every instance of an Polymer 
 element in HTML would be handled as a separate instance code-wise. For me, 
 it would have been more intuitive that properties are "fresh", except I 
 declare them explicitly to be static. (Since ES6 is moving Javascript more 
 towards OOP, I'd like to see the Polymer team to at least consider making 
 Polymer attributes non-static by default.) 

 On Friday, March 18, 2016 at 4:08:59 PM UTC+1, Karl Tiedt wrote:
>
> Read the docs on properties and you'll see a statement about using:
>
> value: function() { return []; }
>
> In relation to arrays and objects with the appropriate change to the 
> function.
> On Mar 18, 2016 07:42, "Rob Stone"  wrote:
>
>> I've just discovered something that is a little confusing and was 
>> hoping a polymer expert could explain what is going on :)
>>
>> I've defined an element with an array property (initialised to empty) 
>> with an attach method that then uses 'this.push' to add items to the 
>> array. 
>> If I then create multiple instances of the element, in the browser 
>> debugger 
>> it looks like the array is shared across all of these instances as each 
>> subsequent copy of the element seems to inherit the array values from 
>> previous elements. What's even more confusing is that if I create a 
>> dom-repeat that iterates over the array, it shows the 'correct' values 
>> for 
>> each instance, ie. it seems to be using an array that doesn't have 
>> duplicate values in it.
>>
>> I have a very small test project that shows this problem, however I 
>> haven't got anywhere to host it so cannot put a link up.
>>
>> Cut down code follo

Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[adi . nita]

Hi,

Maybe a bit off-topic, but still related to data binding. What is the 
difference between defining a property inside the properties object, and 
outside of it? For example:

Polymer({ is: 'some-element', properties: { name0: String }, name1: "" });

Both this.name0 and this.name1 are accessible and both are set on the 
some-element object. Both can be used in data bindings, so having [[name1]] 
in a template will work.

Is this behavior documented or explained somewhere?

Thank you.

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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Lars Knudsen]

I think this should rather be explained clearly in the guidelines. It is a
valuable thing when needed

On Jan 4, 2018 07:57,  wrote:

> Totally agree. Many developers won't know this after they finish reading
> the tutorial. It's like learning Python without being warned of the
> differences between class variables and instance variables.
> To keep a shared state across multiple same type of elements, is not a
> daily demand, but will cause potential troubles in a daily work.
>
> On Wednesday, April 12, 2017 at 5:49:07 PM UTC+2, mpa...@ugcloud.ca wrote:
>>
>> I agree fully with Toni, Polymer is designed to help make web components,
>> and I thought the idea of a web component is that is isolated.  This make
>> it easy to test and re-use etc.  If having multiple copies of an element
>> changes the behavior of it that would makes this harder to test and not
>> intuitive.  I can see people not testing multiple copies of their elements,
>> I have created 8 elements and it wasn't until my 9th one I noticed this
>> issue.  I now have to go back and double check everything.
>>
>> I would actually suggest removing the static array (object) option
>> completely, as you can simple use a parent object to handle this kind of
>> situation, and I think this would be the minority of cases anyway.
>>
>> On Sunday, October 23, 2016 at 3:59:14 PM UTC-4, Toni wrote:
>>>
>>> Although this question is a few months old, I ran into this problem just
>>> now and was not able to solve it immediately with the explanation given. So
>>> for anyone still having issues with this, here is the solution (without
>>> telling you to go anywhere else and try to find it in the documentation...):
>>>
>>> 1. By default, properties of Polymer objects are shared across all
>>> instances of the object (or, to be more precise, all references to the
>>> object, since Polymer doesn't create new instances, as in "new Element()").
>>> Basically, all properties are by default static.
>>> 2. Every property that is supposed to be individual to the specific
>>> reference, in other words, be not static, and changable without messing
>>> with any other instance/reference, has to have the field "value: function()
>>> { return []; }".
>>> 3. Example:
>>>
>>> Polymer({
>>> is: 'txt-carousel-view',
>>> properties: {
>>> myOwnList: {
>>> value: function() { return []; } // this is a non-static
>>> array, invididual and fresh for every instance
>>> },
>>> mySharedList: {
>>> value: []; // this is a static array, shared with every
>>> instance array
>>> }
>>> }
>>> })
>>>
>>> As a Polymer newbie, I assumed that every instance of an Polymer element
>>> in HTML would be handled as a separate instance code-wise. For me, it would
>>> have been more intuitive that properties are "fresh", except I declare them
>>> explicitly to be static. (Since ES6 is moving Javascript more towards OOP,
>>> I'd like to see the Polymer team to at least consider making Polymer
>>> attributes non-static by default.)
>>>
>>> On Friday, March 18, 2016 at 4:08:59 PM UTC+1, Karl Tiedt wrote:

 Read the docs on properties and you'll see a statement about using:

 value: function() { return []; }

 In relation to arrays and objects with the appropriate change to the
 function.
 On Mar 18, 2016 07:42, "Rob Stone"  wrote:

> I've just discovered something that is a little confusing and was
> hoping a polymer expert could explain what is going on :)
>
> I've defined an element with an array property (initialised to empty)
> with an attach method that then uses 'this.push' to add items to the 
> array.
> If I then create multiple instances of the element, in the browser 
> debugger
> it looks like the array is shared across all of these instances as each
> subsequent copy of the element seems to inherit the array values from
> previous elements. What's even more confusing is that if I create a
> dom-repeat that iterates over the array, it shows the 'correct' values for
> each instance, ie. it seems to be using an array that doesn't have
> duplicate values in it.
>
> I have a very small test project that shows this problem, however I
> haven't got anywhere to host it so cannot put a link up.
>
> Cut down code follows:
>
> 
> 
> 
> 
> [[item]]
> 
> 
>
>
> 
> (function () {
> Polymer({
> is: 'test-element',
> properties: {
> items: {
> type: Array,
> value: []
> }
> },
>
>
> attached: function () {
> console.log('attached');
> this.push('items', "1");
> this.push('items', "2");
> 

Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[lkaihua]

Totally agree. Many developers won't know this after they finish reading 
the tutorial. It's like learning Python without being warned of the 
differences between class variables and instance variables.
To keep a shared state across multiple same type of elements, is not a 
daily demand, but will cause potential troubles in a daily work.

On Wednesday, April 12, 2017 at 5:49:07 PM UTC+2, mpa...@ugcloud.ca wrote:
>
> I agree fully with Toni, Polymer is designed to help make web components, 
> and I thought the idea of a web component is that is isolated.  This make 
> it easy to test and re-use etc.  If having multiple copies of an element 
> changes the behavior of it that would makes this harder to test and not 
> intuitive.  I can see people not testing multiple copies of their elements, 
> I have created 8 elements and it wasn't until my 9th one I noticed this 
> issue.  I now have to go back and double check everything.
>
> I would actually suggest removing the static array (object) option 
> completely, as you can simple use a parent object to handle this kind of 
> situation, and I think this would be the minority of cases anyway.
>
> On Sunday, October 23, 2016 at 3:59:14 PM UTC-4, Toni wrote:
>>
>> Although this question is a few months old, I ran into this problem just 
>> now and was not able to solve it immediately with the explanation given. So 
>> for anyone still having issues with this, here is the solution (without 
>> telling you to go anywhere else and try to find it in the documentation...):
>>
>> 1. By default, properties of Polymer objects are shared across all 
>> instances of the object (or, to be more precise, all references to the 
>> object, since Polymer doesn't create new instances, as in "new Element()"). 
>> Basically, all properties are by default static. 
>> 2. Every property that is supposed to be individual to the specific 
>> reference, in other words, be not static, and changable without messing 
>> with any other instance/reference, has to have the field "value: function() 
>> { return []; }". 
>> 3. Example: 
>>
>> Polymer({
>> is: 'txt-carousel-view',
>> properties: {
>> myOwnList: {
>> value: function() { return []; } // this is a non-static 
>> array, invididual and fresh for every instance 
>> },
>> mySharedList: {
>> value: []; // this is a static array, shared with every 
>> instance array
>> }
>> }
>> })
>>  
>> As a Polymer newbie, I assumed that every instance of an Polymer element 
>> in HTML would be handled as a separate instance code-wise. For me, it would 
>> have been more intuitive that properties are "fresh", except I declare them 
>> explicitly to be static. (Since ES6 is moving Javascript more towards OOP, 
>> I'd like to see the Polymer team to at least consider making Polymer 
>> attributes non-static by default.) 
>>
>> On Friday, March 18, 2016 at 4:08:59 PM UTC+1, Karl Tiedt wrote:
>>>
>>> Read the docs on properties and you'll see a statement about using:
>>>
>>> value: function() { return []; }
>>>
>>> In relation to arrays and objects with the appropriate change to the 
>>> function.
>>> On Mar 18, 2016 07:42, "Rob Stone"  wrote:
>>>
 I've just discovered something that is a little confusing and was 
 hoping a polymer expert could explain what is going on :)

 I've defined an element with an array property (initialised to empty) 
 with an attach method that then uses 'this.push' to add items to the 
 array. 
 If I then create multiple instances of the element, in the browser 
 debugger 
 it looks like the array is shared across all of these instances as each 
 subsequent copy of the element seems to inherit the array values from 
 previous elements. What's even more confusing is that if I create a 
 dom-repeat that iterates over the array, it shows the 'correct' values for 
 each instance, ie. it seems to be using an array that doesn't have 
 duplicate values in it.

 I have a very small test project that shows this problem, however I 
 haven't got anywhere to host it so cannot put a link up.

 Cut down code follows:

 
 
 
 
 [[item]]
 
 


 
 (function () {
 Polymer({
 is: 'test-element',
 properties: {
 items: {
 type: Array,
 value: []
 }
 },


 attached: function () {
 console.log('attached');
 this.push('items', "1");
 this.push('items', "2");
 this.push('items', "3");
 console.log('items=' + this.items); // The 1st 
 instance of the element displays 'items=1,2,3' the 2nd displays 
 'items=1,2,3,1,2,3' 
   

Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[mpavlis]

I agree fully with Toni, Polymer is designed to help make web components, 
and I thought the idea of a web component is that is isolated.  This make 
it easy to test and re-use etc.  If having multiple copies of an element 
changes the behavior of it that would makes this harder to test and not 
intuitive.  I can see people not testing multiple copies of their elements, 
I have created 8 elements and it wasn't until my 9th one I noticed this 
issue.  I now have to go back and double check everything.

I would actually suggest removing the static array (object) option 
completely, as you can simple use a parent object to handle this kind of 
situation, and I think this would be the minority of cases anyway.

On Sunday, October 23, 2016 at 3:59:14 PM UTC-4, Toni wrote:
>
> Although this question is a few months old, I ran into this problem just 
> now and was not able to solve it immediately with the explanation given. So 
> for anyone still having issues with this, here is the solution (without 
> telling you to go anywhere else and try to find it in the documentation...):
>
> 1. By default, properties of Polymer objects are shared across all 
> instances of the object (or, to be more precise, all references to the 
> object, since Polymer doesn't create new instances, as in "new Element()"). 
> Basically, all properties are by default static. 
> 2. Every property that is supposed to be individual to the specific 
> reference, in other words, be not static, and changable without messing 
> with any other instance/reference, has to have the field "value: function() 
> { return []; }". 
> 3. Example: 
>
> Polymer({
> is: 'txt-carousel-view',
> properties: {
> myOwnList: {
> value: function() { return []; } // this is a non-static 
> array, invididual and fresh for every instance 
> },
> mySharedList: {
> value: []; // this is a static array, shared with every 
> instance array
> }
> }
> })
>  
> As a Polymer newbie, I assumed that every instance of an Polymer element 
> in HTML would be handled as a separate instance code-wise. For me, it would 
> have been more intuitive that properties are "fresh", except I declare them 
> explicitly to be static. (Since ES6 is moving Javascript more towards OOP, 
> I'd like to see the Polymer team to at least consider making Polymer 
> attributes non-static by default.) 
>
> On Friday, March 18, 2016 at 4:08:59 PM UTC+1, Karl Tiedt wrote:
>>
>> Read the docs on properties and you'll see a statement about using:
>>
>> value: function() { return []; }
>>
>> In relation to arrays and objects with the appropriate change to the 
>> function.
>> On Mar 18, 2016 07:42, "Rob Stone"  wrote:
>>
>>> I've just discovered something that is a little confusing and was hoping 
>>> a polymer expert could explain what is going on :)
>>>
>>> I've defined an element with an array property (initialised to empty) 
>>> with an attach method that then uses 'this.push' to add items to the array. 
>>> If I then create multiple instances of the element, in the browser debugger 
>>> it looks like the array is shared across all of these instances as each 
>>> subsequent copy of the element seems to inherit the array values from 
>>> previous elements. What's even more confusing is that if I create a 
>>> dom-repeat that iterates over the array, it shows the 'correct' values for 
>>> each instance, ie. it seems to be using an array that doesn't have 
>>> duplicate values in it.
>>>
>>> I have a very small test project that shows this problem, however I 
>>> haven't got anywhere to host it so cannot put a link up.
>>>
>>> Cut down code follows:
>>>
>>> 
>>> 
>>> 
>>> 
>>> [[item]]
>>> 
>>> 
>>>
>>>
>>> 
>>> (function () {
>>> Polymer({
>>> is: 'test-element',
>>> properties: {
>>> items: {
>>> type: Array,
>>> value: []
>>> }
>>> },
>>>
>>>
>>> attached: function () {
>>> console.log('attached');
>>> this.push('items', "1");
>>> this.push('items', "2");
>>> this.push('items', "3");
>>> console.log('items=' + this.items); // The 1st instance 
>>> of the element displays 'items=1,2,3' the 2nd displays 'items=1,2,3,1,2,3' 
>>> 
>>> }
>>> });
>>> })();
>>> 
>>> 
>>>
>>> 
>>> 
>>> instance test
>>> >> src="bower_components/webcomponentsjs/webcomponents-list.min.js">
>>> 
>>> 
>>> 
>>> One
>>> Two
>>> 
>>> 
>>>
>>>
>>>
>>> I'm hoping this is a simple misunderstanding on my part, but it does 
>>> have some slightly annoying implications for a project I am working on.
>>>
>>> Rob
>>>
>>> Follow Polymer on Google+: plus.google.com/107187849809354688692
>>> --- 
>>> You received this message because you are subscribed to the Google 
>>>

Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Lars Knudsen]

On Sun, Oct 23, 2016 at 10:12 PM, Daniel Llewellyn 
wrote:

>
>
> On Sun, 23 Oct 2016 at 20:59 Toni  wrote:
>
>> 1. By default, properties of Polymer objects are shared across all
>> instances of the object (or, to be more precise, all references to the
>> object, since Polymer doesn't create new instances, as in "new Element()").
>> Basically, all properties are by default static.
>>
>
> This is not quite accurate.
>
>
>> 2. Every property that is supposed to be individual to the specific
>> reference, in other words, be not static, and changable without messing
>> with any other instance/reference, has to have the field "value: function()
>> { return []; }".
>>
>
> This is only required for Arrays and Objects.
>
> Explanation:
>
> In Javascript all variables are passed-by-value. The variable "holding" an
> Object doesn't actually hold the Object; it only holds a reference to the
> Object in memory. Whereas a variable pertaining to a primitive type
> actually holds the value rather than a reference to the value in memory.
>
> When Polymer creates a new instance of your element it copies the
> prototype into a new Object. When the variable is copied the value is
> copied and passed-by-value but as the value is actually a reference to the
> original Object then the new instance will use the same object as all other
> instances.
>

.. making it (somewhat) possible to make e.g. behaviors that act like a
(singleton) service - like in angular.  As long as you don't reassign any
full object/array to the ones that should live a shared life.


>
> This is a problem with Javascript in general and not specific to Polymer.
>
..or "the quirks of javascript came to the rescue as polymer doesn't have
other (known to me at least :)) ways of replicating angular (singleton)
services" :)

- Lars


>
> Dan.
>
> Follow Polymer on Google+: plus.google.com/107187849809354688692
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> .
>
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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Daniel Llewellyn]

On Sun, 23 Oct 2016 at 20:59 Toni  wrote:

> 1. By default, properties of Polymer objects are shared across all
> instances of the object (or, to be more precise, all references to the
> object, since Polymer doesn't create new instances, as in "new Element()").
> Basically, all properties are by default static.
>

This is not quite accurate.


> 2. Every property that is supposed to be individual to the specific
> reference, in other words, be not static, and changable without messing
> with any other instance/reference, has to have the field "value: function()
> { return []; }".
>

This is only required for Arrays and Objects.

Explanation:

In Javascript all variables are passed-by-value. The variable "holding" an
Object doesn't actually hold the Object; it only holds a reference to the
Object in memory. Whereas a variable pertaining to a primitive type
actually holds the value rather than a reference to the value in memory.

When Polymer creates a new instance of your element it copies the prototype
into a new Object. When the variable is copied the value is copied and
passed-by-value but as the value is actually a reference to the original
Object then the new instance will use the same object as all other
instances.

This is a problem with Javascript in general and not specific to Polymer.

Dan.

Follow Polymer on Google+: plus.google.com/107187849809354688692
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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Toni]

Although this question is a few months old, I ran into this problem just 
now and was not able to solve it immediately with the explanation given. So 
for anyone still having issues with this, here is the solution (without 
telling you to go anywhere else and try to find it in the documentation...):

1. By default, properties of Polymer objects are shared across all 
instances of the object (or, to be more precise, all references to the 
object, since Polymer doesn't create new instances, as in "new Element()"). 
Basically, all properties are by default static. 
2. Every property that is supposed to be individual to the specific 
reference, in other words, be not static, and changable without messing 
with any other instance/reference, has to have the field "value: function() 
{ return []; }". 
3. Example: 

Polymer({
is: 'txt-carousel-view',
properties: {
myOwnList: {
value: function() { return []; } // this is a non-static array, 
invididual and fresh for every instance 
},
mySharedList: {
value: []; // this is a static array, shared with every 
instance array
}
}
})
 
As a Polymer newbie, I assumed that every instance of an Polymer element in 
HTML would be handled as a separate instance code-wise. For me, it would 
have been more intuitive that properties are "fresh", except I declare them 
explicitly to be static. (Since ES6 is moving Javascript more towards OOP, 
I'd like to see the Polymer team to at least consider making Polymer 
attributes non-static by default.) 

On Friday, March 18, 2016 at 4:08:59 PM UTC+1, Karl Tiedt wrote:
>
> Read the docs on properties and you'll see a statement about using:
>
> value: function() { return []; }
>
> In relation to arrays and objects with the appropriate change to the 
> function.
> On Mar 18, 2016 07:42, "Rob Stone" > 
> wrote:
>
>> I've just discovered something that is a little confusing and was hoping 
>> a polymer expert could explain what is going on :)
>>
>> I've defined an element with an array property (initialised to empty) 
>> with an attach method that then uses 'this.push' to add items to the array. 
>> If I then create multiple instances of the element, in the browser debugger 
>> it looks like the array is shared across all of these instances as each 
>> subsequent copy of the element seems to inherit the array values from 
>> previous elements. What's even more confusing is that if I create a 
>> dom-repeat that iterates over the array, it shows the 'correct' values for 
>> each instance, ie. it seems to be using an array that doesn't have 
>> duplicate values in it.
>>
>> I have a very small test project that shows this problem, however I 
>> haven't got anywhere to host it so cannot put a link up.
>>
>> Cut down code follows:
>>
>> 
>> 
>> 
>> 
>> [[item]]
>> 
>> 
>>
>>
>> 
>> (function () {
>> Polymer({
>> is: 'test-element',
>> properties: {
>> items: {
>> type: Array,
>> value: []
>> }
>> },
>>
>>
>> attached: function () {
>> console.log('attached');
>> this.push('items', "1");
>> this.push('items', "2");
>> this.push('items', "3");
>> console.log('items=' + this.items); // The 1st instance 
>> of the element displays 'items=1,2,3' the 2nd displays 'items=1,2,3,1,2,3' 
>> 
>> }
>> });
>> })();
>> 
>> 
>>
>> 
>> 
>> instance test
>> > src="bower_components/webcomponentsjs/webcomponents-list.min.js">
>> 
>> 
>> 
>> One
>> Two
>> 
>> 
>>
>>
>>
>> I'm hoping this is a simple misunderstanding on my part, but it does have 
>> some slightly annoying implications for a project I am working on.
>>
>> Rob
>>
>> Follow Polymer on Google+: plus.google.com/107187849809354688692
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>> 
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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

['Justin Fagnani' via Polymer]

There's really no way to do that. Critically, there's no way to fully clone
an object.
On Mar 18, 2016 9:57 AM, "Rob Stone"  wrote:

> Would it be feasible for polymer to auto-wrap array/object types in a
> function call? I can't imagine anyone wanting the existing behaviour - but
> if this was deemed to be necessary, then a new 'disableAutoWrap' option
> could be added to the type definition object?
>
>
> On Friday, 18 March 2016 16:13:54 UTC, Karl Tiedt wrote:
>>
>> It is how Javascript has always worked... Arrays and Objects are by
>> reference, so in this situation, you have to return a new instance to get
>> that separation.
>>
>> In other libraries this was usually handled in the constructor with
>> this.varname = []; but in Polymer, if you want to handle it in the
>> properties definition (recommended way) requires the function call.
>>
>> -Karl Tiedt
>>
>> On Fri, Mar 18, 2016 at 9:00 AM, Rob Stone  wrote:
>>
>>> Thinking about the mechanics of this, I can now see why it works this
>>> way. However, it is still a pretty nasty gotcha and it might be worth
>>> looking at that area of the documentation and making this issue a bit more
>>> obvious.
>>>
>>> Follow Polymer on Google+: plus.google.com/107187849809354688692
>>> ---
>>> You received this message because you are subscribed to the Google
>>> Groups "Polymer" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to polymer-dev...@googlegroups.com.
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>>> 
>>> .
>>>
>>> For more options, visit https://groups.google.com/d/optout.
>>>
>>
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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Karl Tiedt]

Read the docs on properties and you'll see a statement about using:

value: function() { return []; }

In relation to arrays and objects with the appropriate change to the
function.
On Mar 18, 2016 07:42, "Rob Stone"  wrote:

> I've just discovered something that is a little confusing and was hoping a
> polymer expert could explain what is going on :)
>
> I've defined an element with an array property (initialised to empty) with
> an attach method that then uses 'this.push' to add items to the array. If I
> then create multiple instances of the element, in the browser debugger it
> looks like the array is shared across all of these instances as each
> subsequent copy of the element seems to inherit the array values from
> previous elements. What's even more confusing is that if I create a
> dom-repeat that iterates over the array, it shows the 'correct' values for
> each instance, ie. it seems to be using an array that doesn't have
> duplicate values in it.
>
> I have a very small test project that shows this problem, however I
> haven't got anywhere to host it so cannot put a link up.
>
> Cut down code follows:
>
> 
> 
> 
> 
> [[item]]
> 
> 
>
>
> 
> (function () {
> Polymer({
> is: 'test-element',
> properties: {
> items: {
> type: Array,
> value: []
> }
> },
>
>
> attached: function () {
> console.log('attached');
> this.push('items', "1");
> this.push('items', "2");
> this.push('items', "3");
> console.log('items=' + this.items); // The 1st instance
> of the element displays 'items=1,2,3' the 2nd displays 'items=1,2,3,1,2,3'
> 
> }
> });
> })();
> 
> 
>
> 
> 
> instance test
>  src="bower_components/webcomponentsjs/webcomponents-list.min.js">
> 
> 
> 
> One
> Two
> 
> 
>
>
>
> I'm hoping this is a simple misunderstanding on my part, but it does have
> some slightly annoying implications for a project I am working on.
>
> Rob
>
> Follow Polymer on Google+: plus.google.com/107187849809354688692
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> 
> .
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>

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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Rob Stone]

It's not so much the effort of adding the function call, more that the 
problem (when it occurs) isn't particularly obvious. Hopefully this thread 
will come up in google searches to help the next person that comes across 
this issue :)

On Friday, 18 March 2016 17:03:52 UTC, Karl Tiedt wrote:
>
> I cant imagine adding code to prevent a native JS feature will happen... 
> and sometimes this effect *is* desired. Is adding a 1 line function that 
> much trouble? This is the first complaint I can remember about this. 
> However if you feel that strongly about it, I encourage you to file an 
> issue on the Polymer/Polymer  
> github repo
>
> -Karl Tiedt
>
> On Fri, Mar 18, 2016 at 9:56 AM, Rob Stone  > wrote:
>
>> Would it be feasible for polymer to auto-wrap array/object types in a 
>> function call? I can't imagine anyone wanting the existing behaviour - but 
>> if this was deemed to be necessary, then a new 'disableAutoWrap' option 
>> could be added to the type definition object?
>>
>>
>> On Friday, 18 March 2016 16:13:54 UTC, Karl Tiedt wrote:
>>>
>>> It is how Javascript has always worked... Arrays and Objects are by 
>>> reference, so in this situation, you have to return a new instance to get 
>>> that separation.
>>>
>>> In other libraries this was usually handled in the constructor with 
>>> this.varname = []; but in Polymer, if you want to handle it in the 
>>> properties definition (recommended way) requires the function call.
>>>
>>> -Karl Tiedt
>>>
>>> On Fri, Mar 18, 2016 at 9:00 AM, Rob Stone  wrote:
>>>
 Thinking about the mechanics of this, I can now see why it works this 
 way. However, it is still a pretty nasty gotcha and it might be worth 
 looking at that area of the documentation and making this issue a bit more 
 obvious.

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 .

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>>>
>>> Follow Polymer on Google+: plus.google.com/107187849809354688692
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>>  
>> 
>> .
>>
>> For more options, visit https://groups.google.com/d/optout.
>>
>
>

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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Rob Stone]

Thinking about the mechanics of this, I can now see why it works this way. 
However, it is still a pretty nasty gotcha and it might be worth looking at 
that area of the documentation and making this issue a bit more obvious.

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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Karl Tiedt]

I cant imagine adding code to prevent a native JS feature will happen...
and sometimes this effect *is* desired. Is adding a 1 line function that
much trouble? This is the first complaint I can remember about this.
However if you feel that strongly about it, I encourage you to file an
issue on the Polymer/Polymer 
github repo

-Karl Tiedt

On Fri, Mar 18, 2016 at 9:56 AM, Rob Stone  wrote:

> Would it be feasible for polymer to auto-wrap array/object types in a
> function call? I can't imagine anyone wanting the existing behaviour - but
> if this was deemed to be necessary, then a new 'disableAutoWrap' option
> could be added to the type definition object?
>
>
> On Friday, 18 March 2016 16:13:54 UTC, Karl Tiedt wrote:
>>
>> It is how Javascript has always worked... Arrays and Objects are by
>> reference, so in this situation, you have to return a new instance to get
>> that separation.
>>
>> In other libraries this was usually handled in the constructor with
>> this.varname = []; but in Polymer, if you want to handle it in the
>> properties definition (recommended way) requires the function call.
>>
>> -Karl Tiedt
>>
>> On Fri, Mar 18, 2016 at 9:00 AM, Rob Stone  wrote:
>>
>>> Thinking about the mechanics of this, I can now see why it works this
>>> way. However, it is still a pretty nasty gotcha and it might be worth
>>> looking at that area of the documentation and making this issue a bit more
>>> obvious.
>>>
>>> Follow Polymer on Google+: plus.google.com/107187849809354688692
>>> ---
>>> You received this message because you are subscribed to the Google
>>> Groups "Polymer" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to polymer-dev...@googlegroups.com.
>>> To view this discussion on the web visit
>>> https://groups.google.com/d/msgid/polymer-dev/08b6ea93-1fde-4d29-8271-71b5cf859343%40googlegroups.com
>>> 
>>> .
>>>
>>> For more options, visit https://groups.google.com/d/optout.
>>>
>>
>> Follow Polymer on Google+: plus.google.com/107187849809354688692
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>
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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Rob Stone]

Would it be feasible for polymer to auto-wrap array/object types in a 
function call? I can't imagine anyone wanting the existing behaviour - but 
if this was deemed to be necessary, then a new 'disableAutoWrap' option 
could be added to the type definition object?


On Friday, 18 March 2016 16:13:54 UTC, Karl Tiedt wrote:
>
> It is how Javascript has always worked... Arrays and Objects are by 
> reference, so in this situation, you have to return a new instance to get 
> that separation.
>
> In other libraries this was usually handled in the constructor with 
> this.varname = []; but in Polymer, if you want to handle it in the 
> properties definition (recommended way) requires the function call.
>
> -Karl Tiedt
>
> On Fri, Mar 18, 2016 at 9:00 AM, Rob Stone  > wrote:
>
>> Thinking about the mechanics of this, I can now see why it works this 
>> way. However, it is still a pretty nasty gotcha and it might be worth 
>> looking at that area of the documentation and making this issue a bit more 
>> obvious.
>>
>> Follow Polymer on Google+: plus.google.com/107187849809354688692
>> --- 
>> You received this message because you are subscribed to the Google Groups 
>> "Polymer" group.
>> To unsubscribe from this group and stop receiving emails from it, send an 
>> email to polymer-dev...@googlegroups.com .
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/polymer-dev/08b6ea93-1fde-4d29-8271-71b5cf859343%40googlegroups.com
>>  
>> 
>> .
>>
>> For more options, visit https://groups.google.com/d/optout.
>>
>
>

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[polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Rob Stone]

I've just discovered something that is a little confusing and was hoping a 
polymer expert could explain what is going on :)

I've defined an element with an array property (initialised to empty) with 
an attach method that then uses 'this.push' to add items to the array. If I 
then create multiple instances of the element, in the browser debugger it 
looks like the array is shared across all of these instances as each 
subsequent copy of the element seems to inherit the array values from 
previous elements. What's even more confusing is that if I create a 
dom-repeat that iterates over the array, it shows the 'correct' values for 
each instance, ie. it seems to be using an array that doesn't have 
duplicate values in it.

I have a very small test project that shows this problem, however I haven't 
got anywhere to host it so cannot put a link up.

Cut down code follows:





[[item]]





(function () {
Polymer({
is: 'test-element',
properties: {
items: {
type: Array,
value: []
}
},


attached: function () {
console.log('attached');
this.push('items', "1");
this.push('items', "2");
this.push('items', "3");
console.log('items=' + this.items); // The 1st instance of 
the element displays 'items=1,2,3' the 2nd displays 'items=1,2,3,1,2,3' 
}
});
})();





instance test




One
Two





I'm hoping this is a simple misunderstanding on my part, but it does have 
some slightly annoying implications for a project I am working on.

Rob

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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Rob Stone]

Issue raised 7 months ago, if only the console.warn mentioned there had 
been implemented ;)
https://github.com/Polymer/polymer/issues/2240

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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Karl Tiedt]

It is how Javascript has always worked... Arrays and Objects are by
reference, so in this situation, you have to return a new instance to get
that separation.

In other libraries this was usually handled in the constructor with
this.varname = []; but in Polymer, if you want to handle it in the
properties definition (recommended way) requires the function call.

-Karl Tiedt

On Fri, Mar 18, 2016 at 9:00 AM, Rob Stone  wrote:

> Thinking about the mechanics of this, I can now see why it works this way.
> However, it is still a pretty nasty gotcha and it might be worth looking at
> that area of the documentation and making this issue a bit more obvious.
>
> Follow Polymer on Google+: plus.google.com/107187849809354688692
> ---
> You received this message because you are subscribed to the Google Groups
> "Polymer" group.
> To unsubscribe from this group and stop receiving emails from it, send an
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> 
> .
>
> For more options, visit https://groups.google.com/d/optout.
>

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Re: [polymer-dev] Multiple instances of elements seem to be sharing property values ?

[Rob Stone]

Ouch !!! Thanks Karl, that's a really nasty gotcha, would be interested to 
hear from the polymer team why this is necessary.

On Friday, 18 March 2016 15:08:59 UTC, Karl Tiedt wrote:
>
> Read the docs on properties and you'll see a statement about using:
>
> value: function() { return []; }
>
> In relation to arrays and objects with the appropriate change to the 
> function.
> On Mar 18, 2016 07:42, "Rob Stone" > 
> wrote:
>
>> I've just discovered something that is a little confusing and was hoping 
>> a polymer expert could explain what is going on :)
>>
>> I've defined an element with an array property (initialised to empty) 
>> with an attach method that then uses 'this.push' to add items to the array. 
>> If I then create multiple instances of the element, in the browser debugger 
>> it looks like the array is shared across all of these instances as each 
>> subsequent copy of the element seems to inherit the array values from 
>> previous elements. What's even more confusing is that if I create a 
>> dom-repeat that iterates over the array, it shows the 'correct' values for 
>> each instance, ie. it seems to be using an array that doesn't have 
>> duplicate values in it.
>>
>> I have a very small test project that shows this problem, however I 
>> haven't got anywhere to host it so cannot put a link up.
>>
>> Cut down code follows:
>>
>> 
>> 
>> 
>> 
>> [[item]]
>> 
>> 
>>
>>
>> 
>> (function () {
>> Polymer({
>> is: 'test-element',
>> properties: {
>> items: {
>> type: Array,
>> value: []
>> }
>> },
>>
>>
>> attached: function () {
>> console.log('attached');
>> this.push('items', "1");
>> this.push('items', "2");
>> this.push('items', "3");
>> console.log('items=' + this.items); // The 1st instance 
>> of the element displays 'items=1,2,3' the 2nd displays 'items=1,2,3,1,2,3' 
>> 
>> }
>> });
>> })();
>> 
>> 
>>
>> 
>> 
>> instance test
>> > src="bower_components/webcomponentsjs/webcomponents-list.min.js">
>> 
>> 
>> 
>> One
>> Two
>> 
>> 
>>
>>
>>
>> I'm hoping this is a simple misunderstanding on my part, but it does have 
>> some slightly annoying implications for a project I am working on.
>>
>> Rob
>>
>> Follow Polymer on Google+: plus.google.com/107187849809354688692
>> --- 
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>>  
>> 
>> .
>> For more options, visit https://groups.google.com/d/optout.
>>
>

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