对关联数组对象中的JavaScript foreach循环 [英] Javascript foreach loop on associative array object

问题描述

为什么我的for-each循环不遍历我的JavaScript关联数组对象？

Why my for for-each loop is not iterating over my JavaScript associative array object?

// defining an array
var array = [];

// assigning values to corresponding keys
array["Main"] = "Main page";
array["Guide"] = "Guide page";
array["Articles"] = "Articles page";
array["Forum"] = "Forum board";

// expected: loop over every item,
// yet it logs only "last" assigned value - "Forum"
for (var i = 0; i < array.length; i++) {
    console.log(i);
}

编辑：jQuery的每（）可能会有所帮助：的https：/ /api.jquery.com/jQuery.each/

推荐答案

的。长度属性只跟踪性能与数字索引（键）。您使用字符串键。

The .length property only tracks properties with numeric indexes (keys). You're using strings for keys.

您可以这样做：

var arr_jq_TabContents = {}; // no need for an array

arr_jq_TabContents["Main"] = jq_TabContents_Mian;
arr_jq_TabContents["Guide"] = jq_TabContents_Guide;
arr_jq_TabContents["Articles"] = jq_TabContents_Articles;
arr_jq_TabContents["Forum"] = jq_TabContents_Forum;

for (var key in arr_jq_TabContents) {
    console.log(arr_jq_TabContents[key]);
}

为了安全起见，它在这样的循环是一个好主意，以确保没有任何属性都继承意想不到的结果：

To be safe, it's a good idea in loops like that to make sure that none of the properties are unexpected results of inheritance:

for (var key in arr_jq_TabContents) {
  if (arr_jq_TabContents.hasOwnProperty(key))
    console.log(arr_jq_TabContents[key]);
}

的修改的＆MDASH;它可能是一个好主意，现在要注意的是， Object.keys（）功能在现代浏览器和节点等。该函数返回一个对象的自己的钥匙作为一个数组：

edit — it's probably a good idea now to note that the Object.keys() function is available on modern browsers and in Node etc. That function returns the "own" keys of an object, as an array:

Object.keys(arr_jq_TabContents).forEach(function(key, index) {
  console.log(this[key]);
}, arr_jq_TabContents);

传递给 .forEach（）被称为与每个键和返回的数组中的关键指数Object.keys（回调函数） 。它也通过了，通过该功能遍历数组，但数组不是我们真正有用的;我们需要原始的对象的。可以直接通过名称来访问，但（在我看来）这是一个更好一点，以通过传递第二个参数 .forEach（）显式地传递，这是做＆MDASH ;原始物体MDASH;这将回调内部的约束这个。 （刚看到，这是在下面的注释说明。）

The callback function passed to .forEach() is called with each key and the key's index in the array returned by Object.keys(). It's also passed the array through which the function is iterating, but that array is not really useful to us; we need the original object. That can be accessed directly by name, but (in my opinion) it's a little nicer to pass it explicitly, which is done by passing a second argument to .forEach() — the original object — which will be bound as this inside the callback. (Just saw that this was noted in a comment below.)

这篇关于对关联数组对象中的JavaScript foreach循环的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！