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?
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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.
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