console.log 中的值错误

问题描述

可能的重复:
Chrome 的 JavaScript 控制台是否懒得计算数组?

我在 javascript 中有以下片段，它们的输出让我觉得出了点问题.

I have the following snippets in javascript whose output makes me feel that something is going wrong.

1.

a=2;
console.log(a);
a+=2;
console.log(a);

输出:2 4;正如预期的

Output:2 4 ; as expected

2.

t=[0,2];
console.log(t);
t[0]+=2;
console.log(t);

输出:[2,2] [2,2]

输出不应该是 [0,2] [2,2] ? 以上两种情况有什么区别，导致两种情况的答案不同?

推荐答案

这是因为日志延迟到 Chrome 有时间去做(即您的脚本释放 CPU).

It's because the log is delayed until Chrome has time to do it (i.e. your scripts releases the CPU).

试试这个来了解会发生什么:

Try this to understand what happens :

var t=[0,2];
console.log(t);
setTimeout(function() {
     t[0]+=2;
   console.log(t);
}, 1000);

它输出您期望的内容.

这是Chrome的错误吗?也许是优化的副作用.至少这是一个危险的设计......

Is that a bug of Chrome ? Maybe a side effect of an optimization. At least it's a dangerous design...

为什么会有区别?我想 Chrome 会临时存储它必须记录的内容，在第一种情况下作为主要(不可变)值，在最后一种情况下作为指向数组的指针.

Why is there a difference ? I suppose Chrome stores temporarily what it must log, as a primary (immutable) value in the first case, as a pointer to the array in the last case.

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