为什么([a]，"b"]中的"a")产生假，而([1,2]中的1)产生真? [英] Why does ("a" in ["a","b"]) yield false, and (1 in [1,2]) yield true?

问题描述

可能重复:
运算符中的javascript

为什么([[a]，"b"]中的"a")产生 false 和([1,2]中的1)产生 true 吗?为什么"a" 与该数组的第一个元素不匹配，而1与它匹配呢?为什么它不能与字符串一起使用?

Why does ("a" in ["a","b"]) yield false, and (1 in [1,2]) yield true ? Is there a reason why "a" does not match the first element of that array and 1 does ? Why won't it work with strings ?

推荐答案

- arr ["1"] 是值 2 .例如，在["a"，"b"] 中的 0也是 true .该行为与所使用的字符串或数字无关.

The in operator checks for the existence of properties by key, not by value. And your array of length 2 has an index "1" - arr["1"] is the value 2. For example, also 0 in ["a", "b"] is true. The behaviour does not depend on a string or a number being used.

通常将其用于普通对象，而不是数组.类似于{a:1} === true 中的"a"或{a:1} === false 中的"b".

You usually would use it on plain objects, not on arrays. Like "a" in {a:1} === true, or "b" in {a:1} === false.

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