When is __proto__ useful?

When is __proto__ useful?开发者_如何学JAVA

A lot of browsers support it, but because not all do, programmers seem to be scared of using it. I've never seen it in any code (such as the libraries jQuery and backbone.js).

When is __proto__ useful? Is it just a geeky thing for completeness?

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__proto__ is deprecated and should not be used. Use Object.getPrototypeOf instead. See https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/Proto - But Opera supports __proto__ and not Object.getPrototypeOf, so beware.

That said, Object.getPrototypeOf is, like the name says, used to get the prototype of an object. I've never found this useful yet.

Edit 2012-02-06 Opera supports Object.getPrototypeOf as of 11.60.

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It is useful if you are going to modify an objects prototype and need to find out if it has been already modified.

Note that __proto__ is deprecated, instead you should is Object.getPrototypeOf.

MDN Documentation on proto