JavaScript 中 typeof 和 instanceof 的区别 [英] Differences between typeof and instanceof in JavaScript

问题描述

我正在使用 node.js，所以这可能特定于 V8.

I'm working with node.js, so this could be specific to V8.

我一直注意到 typeof 和 instanceof 之间存在一些奇怪的差异，但这里有一个让我很烦恼的地方:

I've always noticed some weirdness with differences between typeof and instanceof, but here is one that really bugs me:

var foo = 'foo';
console.log(typeof foo);

Output: "string"

console.log(foo instanceof String);

Output: false

那里发生了什么?

推荐答案

typeof 是一种返回"传递给它的任何原始类型的结构.
instanceof 测试右侧操作数是否出现在左侧原型链中的任何位置.

typeof is a construct that "returns" the primitive type of whatever you pass it.
instanceof tests to see if the right operand appears anywhere in the prototype chain of the left.

需要注意的是，字符串字面量 "abc" 和字符串对象 new String("abc") 之间存在巨大差异.在后一种情况下，typeof 将返回object"而不是string".

It is important to note that there is a huge difference between the string literal "abc", and the string object new String("abc"). In the latter case, typeof will return "object" instead of "string".

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