最近在读elementUI源码的时候发现了这样一段代码
isChecked() {
if ({}.toString.call(this.model) === '[object Boolean]') {
return this.model;
} else if (Array.isArray(this.model)) {
return this.model.indexOf(this.label) > -1;
} else if (this.model !== null && this.model !== undefined) {
return this.model === this.trueLabel;
}
},
其中用toString.call()来检测数据类型，这样的方式无疑是比typeOf严谨的，特此记录一下。
typeof null
// "object"
typeof [8]
// "object"
typeof {}
// "object"
typeof function(){}
// "function"
typeof 2
//"number"
typeof ""
//"string"
typeof true
//"boolean"
typeof undefined
//"undefined"
typeof Symbol(2)
typeof 无法区分null 数组和对象.
再看一下instanceof
[] instanceof Array
// true 这种方法可以判断数组，不能区分对象
[] instanceof Object
// true
null instanceof Object
// false 也不能区分null
再看看{}.toString.call()
console.log({}.toString.call(1))//[object Number]
console.log({}.toString.call("11"))//[object String]
console.log({}.toString.call(/123/))//[object RegExp]
console.log({}.toString.call({}))//[object Object]
console.log({}.toString.call(function(){}))//[object Function]
console.log({}.toString.call([]))//[object Array]
console.log({}.toString.call(true))//[object Boolean]
console.log({}.toString.call(new Date()))//[object Date]
console.log({}.toString.call(new Error()))//[object Error]
console.log({}.toString.call(null))//[object Null]
console.log({}.toString.call(undefined))//[object Undefined]
console.log(String(undefined))//undefined
console.log(String(null))//null
稍微封装一下
function isType(type) {
return function(obj) {
return {}.toString.call(obj) == "[object " + type + "]"
}
}
var isObject = isType("Object")
var isString = isType("String")
var isArray = Array.isArray || isType("Array")
var isFunction = isType("Function")
var isUndefined = isType("Undefined")
