无法读取未定义的属性"forEach" [英] Cannot read property 'forEach' of undefined

问题描述

var funcs = []
[1, 2].forEach( (i) => funcs.push( () => i  ) )

为什么会产生以下错误?

Why does it produce the error below?

TypeError: Cannot read property 'forEach' of undefined
    at Object.<anonymous>

但是，如果在第一行的末尾添加分号; ，该错误就会消失.

However, the error goes away if the semicolon ; is added to the end of the first line.

推荐答案

第一行末没有分号.因此这两行同时运行，这被解释为将 funcs 的值设置为

There is no semicolon at the end of the first line. So the two lines run together, and it is interpreted as setting the value of funcs to

[][1, 2].forEach( (i) => funcs.push( () => i  ) )

表达式 1、2 变为 2 (

The expression 1, 2 becomes just 2 (comma operator), so you're trying to access index 2 of an empty array:

[][2] // undefined

并且 undefined 没有 forEach 方法.要解决此问题，请始终确保在行末添加分号(否则，请确保您知道自己在做什么).

And undefined has no forEach method. To fix this, always make sure you put a semicolon at the end of your lines (or if you don't, make sure you know what you're doing).

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