> 1. We want sane isObject and isNull predicates, ideally using typeof. Lack of
> them continues to bite people, as the web contains code that wrongly assumes
> typeof x == "object" => x.foo won't throw on null x.
What are the use cases for typeof? Offhand, I see five and for most of them,
other solutions seem to be better.
1. Checking whether a variable has been declared.
Problematic: verbose and conflated with checking for a declared variable
having the value `undefined`.
Better: a dedicated operator or predicate for performing this check.
2. Checking that a value is neither null nor undefined.
Problematic: can’t be done via only typeof currently.
Better: a predicate for performing this check. This use case will become
less important with default parameter values.
3. Distinguishing between objects and primitives.
Problematic: Made more difficult by typeof null === "object" and typeof
function () {} === "function".
Better: predicates such as isObject() and isPrimitive()
4. Determining the type of a primitive value.
Better: typeof is OK here, but changing it so that typeof null === "null"
would help.
5. Determining the type of a value (primitive or otherwise).
Better: I would want a function, e.g. getTypeName() that works like
(null-enabled) typeof for primitives and returns the value of the [[Class]]
property for objects.
Everything except #1 can be easily implemented as functions (and be brought to
ES5 via shims). A function such the #5 getTypeName() could take care of use
case #4, as well.
Ideas for getTypeName(): http://www.2ality.com/2011/11/improving-typeof.html
--
Dr. Axel Rauschmayer
a...@rauschma.de
home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com
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