angular.is[Array, Date, RegExp, File] ignores prototype chain

[rynz]

Dear Angular Team,

angular.isArray currently uses Object.prototype.toString to determine if a variable is an Array which results, for example, in filters such as orderByFilter ignoring collection classes that inherit properties and methods of Array.prototype. As well as an added performance impact compared to instanceof.

Example: http://jsfiddle.net/M3U3g/
Performance Test: http://jsperf.com/instanceof-vs-object-prototype-tostring-angular

Can we please use instanceof rather than Object.prototype.toString within angular.isArray so orderByFilter and other services work with classes that inherit from Array.prototype?

It may also be worth considering changing isDate, isRegExp and isFile as well for the performance increase and classes that inherit from those prototypes.

[caitp]

instanceof is not particularly fast when the prototype chain is long, and additionally suffers from issues when the array is from a different browsing context/sandbox (which can happen occasionally).

[caitp]

Sorry, didn't mean to close that. But yeah, I'm not sure it's really worthwhile to worry about it. It could be, and perhaps we'll know more once benchpress is usable.

[rynz]

I agree instanceof is slower for large prototype chains, but that's generally a concern of the developer. Angular's framework does not have any large prototype chains that angular.isArray checks upon and unit tests pass.

Can you please be more specific as to the issues Array suffers from in different contexts/sandboxes? instanceof is used often within Angular already.

Personally I have a collection factory that is used to instantiate new collection services. Collection services can be injected into controllers, returned from http promises etc and it works great with Angular. The only pitfall was found today when using orderByFilter I have to re-create the $scope.model as an empty array, loop over the collection service and push each item from the collection into it just to have sorting because the collection service inherits from Array.prototype rather that being an Array directly. Losing all inherited properties / methods of the collection service along the way.

The latest "Crafting the Perfect AngularJS Model" was a great testament to prototypical inheritance but without a collection class that can be sorted, as well as the many other utilities that angular.isArray checks upon we lose so much Angular has to offer.

[caitp]

Can you please be more specific as to the issues Array suffers from in different contexts/sandboxes? instanceof is used often within Angular already.

Every browsing context has its own global object, and its own version of all of the native constructors. This means that when you have to communicate between different browsing contexts (EG with iframes or new windows created via window.open), instanceof Array does not really work, you need to specify the appropriate global object. So that gets ugly for helper methods. And while it's easy to say "my app doesn't depend on this", it has been, and continues to be a problem.

On modern browsers, we can use Array.isArray(), and just keep the low-performance nonsense to the legacy browsers. I think that's probably the best solution, because it works across browsing contexts, and does not depend on crawling the prototype chain or ObjectToString.

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But again, I am skeptical that this is a major bottleneck for anybody, really.

[rynz]

From what I've seen the Polyfill for Array.isArray() is Object.prototype.toString.call(arg) === '[object Array]' and from my tests in Chrome behaves the same way, stating CollectionClass in the example as false.

http://jsfiddle.net/EanR3/

@caitp @IgorMinar Does this mean Angular will never support "Collection Classes" derived from Javascript's Array Prototype?

[caitp]

Objects derived from the Array prototype should have an internal class of Array (at least in v8, and probably mozjs as well), so you probably don't need to worry about that. (So long as the prototype is used and the array constructor is called)

[btford]

Unless you have a perf test showing that this causes some real-world use to Angular to be slow, it's not worth spending time on IMO.

Does this mean Angular will never support "Collection Classes" derived from Javascript's Array Prototype?

Any reason you don't just do:

MyCollection.prototype.toString = function () {
  return '[object Array]';
};