这个最终号码来自哪里？

Question

If I run the following code in Chrome console (apologies for the label):

var x = 0;

theLoop:
    while (1) {

        if (!(x <= 2)) {
            break theLoop;
        }

        console.log('x: ', x);
        ++x;
        continue theLoop;
    }

The following is output to the console:

x:  0
x:  1
x:  2
3

It's late, so I'm missing something very obvious, but where is the '3' coming from?

Answer 1

Don't worry about that: it is not an actual console.log, but just your browser that displays the last value that has been read (unless it is assigned to a var ), in this case the ++x that equals 3.

For instance if at the end of your snippet you add console.log('the end'); or even just 0; the last log will be different, yet won't affect your program.

Answer 2

It looks like Chrome by default prints the last assigned variable, but only when it was assigned at least twice, so this:

 var x = 5; var y = 3; 

will result with nothing, but

var x = 5;
x = 4;
var y = 3;

will give you 4 .

In your case it was x=3

Answer 3

I have seen such too. But the value is not used in application. Firefox won't display it.

Answer 4

好的，所以3是控制台在循环后返回x值，原因x == 3是在显示x: 2行之后， ++x再次递增x ，ergo x == 3 ！