The reason why you use args.This() instead of creating an empty
ValueObject and appending keys to that is partially due to the way the
new operator works in JavaScript when called with a function and
operating in accordance with that when faking JS object creation via C++
functions. Roughly speaking, it does the following (in order):
1) First creates an empty object
2) Sets the new objects hidden prototype field to the function's
prototype member, if there is one. (interpret this loosely, changes
slightly from interpreter to interpreter, but essentially this is what
happens )
3) Sets this to the empty object, and then calls the function body
(making any changes to this happen to the empty object)
The interesting part comes in when you consider the way in which
v8 implements callbacks: you want the callback function to behave like
Normal JS, but v8 function callbacks don't work in quite way you might
expect. You might expect, for instance, that Set would overwrite any
function
present within the object, and that overriding a function declared with
Set would simply get rid of the callback.
From what I believe, the first is true, but I know for sure the second is
not. If you overwrite a function within JS, the overriding function will be
called *before* your function callback, but both will be called. However,
your C++ callback will be the function that actually returns a value. So
in order
to preserve any changes made to this during the callback, you extend
args.This(), and do not simply create a new Object (unless this is what you
desire).
Hope that helps,
Stew
On Mon, Apr 23, 2012 at 9:37 PM, Ben Noordhuis i...@bnoordhuis.nl wrote:
On Tue, Apr 24, 2012 at 02:54, Ryan Cole r...@rycole.com wrote:
I'm wrapping a C++ object and then appending some properties. I'm calling
Wrap(), and then Set()'ing the properties directly onto args.This(). This
does not look or feel right to me, so I'm inclined to think I'm doing it
wrong. I'm so new to this that none of the examples are standing out to
me
as the proper way of doing this.
Can someone please take a peek at the highlighted lines of my code and
give
me a few pointers? Namely, am I doing this incorrectly?
https://github.com/ryancole/node-hdf5/blob/master/src/node_h5file.cc#L67-74
There's nothing really wrong with that approach. If the properties are
subject to change, you could use ObjectTemplate::SetAccessor()
instead.
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