组合数组时无法读取未定义的属性'push' [英] Cannot read property 'push' of undefined when combining arrays

问题描述

当将数组的内容推送到另一个数组时，我得到

When pushing an array's contents to another array I get

未捕获的TypeError：无法读取未定义的属性'push'错误
在此代码段中。

"Uncaught TypeError: Cannot read property 'push' of undefined" error in this snippet.

var order = new Object(), stack = [];
for(var i=0;i<a.length;i++){
    if(parseInt(a[i].daysleft) == 0){ order[0].push(a[i]); }
    if(parseInt(a[i].daysleft) > 0){ order[1].push(a[i]); }
    if(parseInt(a[i].daysleft) < 0){ order[2].push(a[i]); }
}

为什么我会在第二个中出现此错误 非常感谢！

Why do I get this error in the second if statement ? Thanks a lot!

推荐答案

您收到错误，因为 order [1] 是 undefined 。

You get the error because order[1] is undefined.

该错误消息意味着代码中的某处，正在尝试访问具有某个名称的属性（此处为push），而不是对象，引用的基础实际上是 undefined 。因此，要找到问题，您需要查找引用该属性名称（push）的代码，并查看其左侧的内容。在这种情况下，代码是

That error message means that somewhere in your code, an attempt is being made to access a property with some name (here it's "push"), but instead of an object, the base for the reference is actually undefined. Thus, to find the problem, you'd look for code that refers to that property name ("push"), and see what's to the left of it. In this case, the code is

if(parseInt(a[i].daysleft) > 0){ order[1].push(a[i]); }

这意味着代码需要 order [1] 成为一个数组。但是，不是一个数组;它是 undefined ，所以你得到错误。为什么未定义？好吧，根据您提出的问题，您的代码无法做任何事情。

which means that the code expects order[1] to be an array. It is, however, not an array; it's undefined, so you get the error. Why is it undefined? Well, your code doesn't do anything to make it anything else, based on what's in your question.

现在，如果您只想放置 a [i] 在对象的特定属性中，然后根本不需要调用 .push（）：

Now, if you just want to place a[i] in a particular property of the object, then there's no need to call .push() at all:

var order = [], stack = [];
for(var i=0;i<a.length;i++){
    if(parseInt(a[i].daysleft) == 0){ order[0] = a[i]; }
    if(parseInt(a[i].daysleft) > 0){ order[1] = a[i]; }
    if(parseInt(a[i].daysleft) < 0){ order[2] = a[i]; }
}

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