类型错误:无法读取未定义 Javascript 的属性“forEach" [英] TypeError: Cannot read property 'forEach' of undefined Javascript

问题描述

以下是我得到的代码无法读取未定义的属性forEach".

const print2 = function(x, y) {
  console.log(x*y)
}

[1,2,3,4].forEach( x => print2(x, 20) )

让我知道我在这里做错了什么，但如果我这样做 -

Let me know what I am doing wrong here, though if I do -

function print2(x, y) {
  console.log(x*y)
}

[1,2,3,4].forEach( x => print2(x, 20) )

这工作正常.

推荐答案

由于函数后没有分号，代码片段被解释如下:

Since there's no semicolon after the function, the snippet gets interpreted as the following:

const print2 = function(x, y) {
  console.log(x*y)
}[1,2,3,4].forEach( x => print2(x, 20) )

这意味着它正在尝试对函数进行索引.在函数之后或数组字面量之前添加一个分号:

Which means that it's trying to index into the function. Add a semicolon either after the function, or before the array literal:

const print2 = function(x, y) {
  console.log(x*y)
};

[1,2,3,4].forEach( x => print2(x, 20) )

或

const print2 = function(x, y) {
  console.log(x*y)
}

;[1,2,3,4].forEach( x => print2(x, 20) )

在此处详细了解 Javascript 的自动分号插入:JavaScript 的自动分号插入 (ASI) 的规则是什么?

More about Javascript's automatic semicolon insertion here: What are the rules for JavaScript's automatic semicolon insertion (ASI)?

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