在Javascript中，为什么[1,2] == [1,2]或（{a：1}）==（{a：1}）为假？ [英] In Javascript, why is [1, 2] == [1, 2] or ({a : 1}) == ({a : 1}) false?

问题描述

以下是在Firebug中完成的：

The following is done in Firebug:

>>> [1, 2] == [1, 2]
false

>>> ({a : 1}) == ({a : 1})
false

我认为Javscript有一些规则说，如果一个Object或Array对相同的元素有相同的引用，那么它们是相等的吗？

I thought Javscript has some rule that says, if an Object or Array has the same references to the same elements, then they are equal?

但即使我说

>>> foo = {a : 1}
Object { a=1}

>>> [foo] == [foo]
false

>>> ({a: foo}) == ({a: foo})
false

是否有办法使它能够进行元素比较并返回 true ？

Is there a way to make it so that it can do the element comparison and return true?

推荐答案

{} 和 [] 与新对象相同和 new Array

和 new Object！= new对象（与数组同上）因为它们是新的和不同的对象。

And new Object != new Object (ditto with Array) because they are new and different objects.

如果你想知道两个任意对象的内容是否相同，那么快速（但很慢）修复是

If you want to know whether the content of two arbitary objects is the "same" for some value of same then a quick (but slow) fix is

JSON.parse（o）=== JSON.parse（o）

一个更优雅的解决方案定义一个相等的函数（未经测试）

A more elegant solution would be to define an equal function (untested)

var equal = function _equal(a, b) {
  // if `===` or `==` pass then short-circuit
  if (a === b || a == b) { 
    return true;
  }
  // get own properties and prototypes
  var protoA = Object.getPrototypeOf(a), 
      protoB = Object.getPrototypeOf(b),
      keysA = Object.keys(a), 
      keysB = Object.keys(b);

  // if protos not same or number of properties not same then false
  if (keysA.length !== keysB.length || protoA !== protoB) {
    return false;
  }
  // recurse equal check on all values for properties of objects
  return keysA.every(function (key) {
    return _equal(a[key], b[key]);
  });
};

等于示例

警告：写作在所有输入上工作的相等函数很难，一些常见的问题是（null == undefined）=== true 和（NaN = == NaN）=== false 我在我的函数中都没有。

Warning: writing an equality function that "works" on all inputs is hard, some common gotchas are (null == undefined) === true and (NaN === NaN) === false neither of which I gaurd for in my function.

我没有处理任何跨浏览器问题，我只是假设ES5存在。

Nor have I dealt with any cross browser problems, I've just assumed ES5 exists.

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