我可以通过相反的顺序循环javascript对象吗？ [英] Can I loop through a javascript object in reverse order?

问题描述

所以我有一个这样的JavaScript对象：

  foo = {
one：some ，
two：thing，
three：else
}; 
  

我可以这样循环：

<$ p （foo.hasOwnProperty（i））{
//做某事
}
$（$ f $） b $ b

它将以的顺序循环访问一个 3 > 2 > 一个。

问题：对象反转功能。如果是一个数组，我可以使用 unshift 来反向或构建一个新数组，但是当我需要反向循环时，属性。任何想法？

谢谢！

解决方案

Javascript对象没有保证的固有顺序，所以不存在反向顺序。

4.3.3对象对象是Object类型的成员。它是属性的一个无序集合，每个属性都包含一个原始
值，对象或函数。存储在
对象的属性中的函数称为方法。

浏览器似乎返回他们被添加到对象相同的顺序，但由于这不是标准的，你可能不应该依赖这种行为。

一个简单的函数调用每个函数属性和浏览器for..in给出的顺序是相反的：

  // f是一个函数， obj作为'this'和属性名称作为第一个参数
函数reverseForIn（obj，f）{
 var arr = []; 
（var key in obj）{
 //如果需要，添加hasOwnPropertyCheck 
 arr.push（key）; 
 
 for（var i = arr.length-1; i> = 0; i--）{
 f.call（obj，arr [i]）; 
 
 
 $ b // usage 
 reverseForIn（obj，function（key）{console.log（'KEY：'，key，'VALUE：这[key]）;}）; 
  

使用JsBin： http://jsbin.com/aPoBAbE/1/edit

我再次说for..in的顺序是不能保证的，所以相反的顺序是不能保证的。谨慎使用！

So I have a JavaScript object like this:

foo = {
  "one": "some",
  "two": "thing",
  "three": "else"
};

I can loop this like:

for (var i in foo) {
  if (foo.hasOwnProperty(i)) {
    // do something
  }
}

Which will loop through the properties in the order of one > two > three.

However sometimes I need to go through in reverse order, so I would like to do the same loop, but three > two > one.

Question:
Is there an "object-reverse" function. If it was an Array, I could reverse or build a new array with unshift but I'm lost with what to do with an object, when I need to reverse-loop it's properties. Any ideas?

Thanks!

解决方案

Javascript objects don't have a guaranteed inherent order, so there doesn't exist a "reverse" order.

4.3.3 Object An object is a member of the type Object. It is an unordered collection of properties each of which contains a primitive value, object, or function. A function stored in a property of an object is called a method.

Browsers do seem to return the properties in the same order they were added to the object, but since this is not standard, you probably shouldn't rely on this behavior.

A simple function that calls a function for each property in reverse order as that given by the browser's for..in, is this:

// f is a function that has the obj as 'this' and the property name as first parameter
function reverseForIn(obj, f) {
  var arr = [];
  for (var key in obj) {
    // add hasOwnPropertyCheck if needed
    arr.push(key);
  }
  for (var i=arr.length-1; i>=0; i--) {
    f.call(obj, arr[i]);
  }
}

//usage
reverseForIn(obj, function(key){ console.log('KEY:', key, 'VALUE:', this[key]); });

Working JsBin: http://jsbin.com/aPoBAbE/1/edit

Again i say that the order of for..in is not guaranteed, so the reverse order is not guaranteed. Use with caution!

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