为什么这个`do`–`while`循环在结束之后重复最后一个值? [英] Why does this `do`–`while` loop repeat the last value after the end?

问题描述

我在Google Chrome控制台中尝试了以下代码，并获得了此输出.为什么还要再打印4张?

I tried the following code in the Google Chrome console and I’m getting this output. Why is there an additional 4 printed?

var i = 0;

do{
  console.log(i);
  i++;
} while(i < 5);

输出:

0
1
2
3
4
4

推荐答案

最后没有多余的4个.您的循环是正确的，并且可以正常工作:).那是 i ++ 表达式的返回值，您在开发人员控制台中误认为了 console.log .试试这个，您会发现的；

There is no extra 4 at end. Your loop is correct and works just fine :). That's return value of the i++ expression, which you are mistaking for console.log in developer console. Try this, you will figure it out;

var i=0;do{console.log('i = ', i);i++;}while(i<5);

编辑感谢@ggorlen指出这一点，它是block( {} )中最后一个表达式的返回值，即 i ++ ， i 会增加值并返回其最后一个值(如果i = 4； i ++ 会返回4并使i = 5的值)，( ++ i ，返回5，使i = 5)

Edit Thanks to @ggorlen for pointing this out, it's the return value of last expression in block({}) which is i++, i increments the value and returns it's last value (if i = 4; i++ returns 4 and makes value of i = 5), (++i, returns 5 and makes value of i = 5)

var i=0;do{console.log('i = ', i);++i;}while(i<5);

将给出5的返回值

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