Javascript数组日志混乱 [英] Javascript Array logging confusion

问题描述

我注意到一些我不能理解的东西。我在JavaScript中做一些非常简单的事情：

I have noticed something that I cannot understand at all. I am doing something really simple in JavaScript:

var a = [1,2,3];

console.log(a.push(4));
console.log(a);
console.log(a.push(5));

我希望控制台记录： 4 [1,2,3,4] 和 5 此处 。
实际的控制台输出如下： 4 ， [1,2,3,4,5] 和 5

I would expect the console to log: 4, [1,2,3,4], and 5 as described here for example. The catch is that the actual console output looks like: 4, [1,2,3,4,5], and 5

请参阅： http://jsfiddle.net/HknMF/

实际上， 5

What on earth makes the 5 appear in the second log output?

：fwiw这里是Firebug的屏幕截图，显示了两种行为： http://i.imgur.com/fwAK3.png

EDIT: fwiw here's a screenshot of Firebug showing both behaviors: http://i.imgur.com/fwAK3.png

推荐答案

在某些浏览器中的控制台使用对数组/对象的引用，并且在 console.log（）调用后更改的对象会看到已更改的对象。

The console in some browsers uses a reference to the array/object, so when you inspect it and the object changed after the console.log() call you'll see the changed object.

这也发生在对象，但不是为内联显示的数组：

In Firefox this also happens for objects, but not for arrays which are displayed inline anyway:

>>> var a = [1,2,3]; console.log(a.push(4)); console.log(a); console.log(a.push(5));
4
[1, 2, 3, 4]
5

特别是对于不包含函数的对象，快速解决方法是克隆它们（如果你有jQuery，则日志 $。extend（{}，yourObject）字符串版本（那么你失去了好的对象视图，只是得到一个纯字符串）。使用 a.slice（0）

Especially for objects that do not contain functions a quick workaround is either cloning them (log $.extend({}, yourObject) if you have jQuery) or logging their JSON string version (then you lose the nice object view and just get a plain string though). An array can easily cloned (shallow copy!) using a.slice(0)

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