“var variable”返回undefined？ [英] "var variable" returns undefined?

问题描述

当我运行var variable = true;时在Chrome控制台中我得到未定义返回：

When I run "var variable = true;" in chrome console I get "undefined" returned:

> var variable = true;
undefined

但是当我没有var运行时它返回true：

But when I run without "var" it returns true:

> variable = true;
true

为什么用var返回undefined？

Why is it returning "undefined" with "var"?

令人困惑的是因为我预计它会返回true。

It's confusing cause I expected it would return true.

推荐答案

第一个是声明，而第二个是表达。虽然不完全相同，但它类似于C的规则：

The first is a statement, while the second is an expression. While not quite the same, it is similar to C's rules:

// A statement that has no value.
int x = 5;

// An expression...
x = 10;

// ...that can be passed around.
printf("%d\n", x = 15);

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