typeof运算符

In JavaScript, any value has a type assigned.

在JavaScript中，任何值都有分配的类型。

The typeof operator is a unary operator that returns a string representing the type of a variable.

typeof运算符是一元运算符，它返回表示变量类型的字符串。

Example usage:

用法示例：

typeof 1 //'number'typeof '1' //'string'typeof {name: 'Flavio'} //'object'typeof [1, 2, 3] //'object'typeof true //'boolean'typeof undefined //'undefined'typeof (() => {}) //'function'typeof Symbol() //'symbol'

JavaScript has no “function” type, and it seems funny that typeof returns 'function' when we pass it a function.

JavaScript没有“函数”类型，当我们将其传递给函数时， typeof返回'function'似乎很有趣。

It’s one quirk of it, to make our job easier.

这是一个怪癖，使我们的工作更轻松。

If you don’t initialize the variable when you declare it, it will have the undefined value until you assign a value to it.

如果在声明变量时未对其进行初始化，则该变量将具有undefined值，直到您为其分配值为止。

let a //typeof a === 'undefined'

typeof works also on object properties.

typeof也适用于对象属性。

If you have a car object, with just one property:

如果您有一个只有一个属性的car对象：

const car = {  model: 'Fiesta'}

This is how you check if the color property is defined on this object:

这是检查color属性是否在此对象上定义的方法：

if (typeof car.color === 'undefined') {  // color is undefined}

翻译自:

typeof运算符