console.log（myFunction（））返回未定义 [英] console.log(myFunction()) returns undefined

问题描述

我是JavaScript的新手，我尝试使用它来了解所有内容。我写了

I'm new to JavaScript, and I try to play around with it to understand all in-and-outs. I write

function greet() {
    console.log("Hi");
};

console.log(greet());

它在控制台中的结果是

> Hi app.js:2 
> undefined app.js:4

我认为这是因为 greet（）< console.log 中的/ code>首先调用该函数，该函数会打印出 Hi 。我们得到日志的第一行。 但是第二行是哪里来的？

I assume this is because greet() inside console.log first calls the function, which prints out "Hi". We get first line of log. But where did the second line come from?

然后我想是因为 Hi 是 greet（）的整体结果，然后 console.log 的总体结果基本上称为变量 Hi ，但在这种情况下，结果将是未定义，而不是未定义

Then I thought because Hi is overall result of greet(), then console.log basically calls variable Hi, but in this case the result would be is not defined, not undefined

推荐答案

在JavaScript中，如果使用关键字 return 的函数未返回任何内容，则<$

In JavaScript, if nothing is returned from the function with the keyword return then undefined is returned by default.

var data = greet();
console.log(data);// undefined, since your function does not return.

等效于：

console.log（greet（））;

第二个输出是该函数返回的结果。由于您没有从该函数返回任何内容，因此会打印 undefined 。

The second output is the returned result from the function. Since you are not returning anything from the function hence prints undefined.

要在第二个控制台中打印 Hi您必须从函数中返回该值。

To print 'Hi' in the second console you have to return that from the function.

function greet() {
  console.log("Hi");
  return 'Hi';
};

console.log(greet());

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