如果 console.log(4) 在 Chrome 控制台中输出 undefined 是什么意思? [英] What does it mean if console.log(4) outputs undefined in Chrome Console?

问题描述

I used the Chrome Console to write a simple statement:

console.log(4)

and received the Output:

4

undefined

What does the undefined statement mean? Does the undefined statement imply correct execution? If I execute the statement via a separate html file and then look at the console, the output is just 4.

解决方案

The undefined is the return value of console.log(...).

You can see this by defining two functions in the console, one returning something, and the other returning nothing, e.g. like this:

function f1() {
  return 1;
}
function f2() {
  return;
}

And then calling them separately (manually)

f1(); // shows '1'

and

f2(); // shows 'undefined'

Also note the little symbol before these return value string.

这篇关于如果 console.log(4) 在 Chrome 控制台中输出 undefined 是什么意思?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！