大家好，我是小逗号，今天给大家分享一下我们前端JS的类型判断
js类型分为两种
简单类型 : Number , String , Boolean , Undefined , Null ，symbol 。
复杂类型 : object（Array , Function ，Date）。
在我们的内存存储分为堆内存和栈内存，也就是简单类型存储栈，复杂存储堆里面。
呢么我们接下来说一下它们的类型判断。
1. typeof 不可以判断复杂数据类型 复杂数据类型返回Object
let typeof_ = {
isArray:(context)=>typeof context ,
isObject:(context)=>typeof context ,
isString:(context)=>typeof context ,
isNull:(context)=>typeof context ,
isUndefined:(context)=>typeof context ,
isNumber:(context)=>typeof context ,
isBoolean:(context)=>typeof context ,
isFunction:(context)=>typeof context ,
isSymbol:(context)=>typeof context ,
isDate:(context)=>typeof context ,
}
console.log(typeof_.isArray([])); // object
console.log(typeof_.isObject({})); // object
console.log(typeof_.isString("1111")); // string
console.log(typeof_.isNull(null)); // object
console.log(typeof_.isUndefined(undefined)); // undefined
console.log(typeof_.isNumber(111)); // number
console.log(typeof_.isBoolean(true)); // boolean
console.log(typeof_.isFunction(new Function())); // function
console.log(typeof_.isSymbol(Symbol())); // symbol
console.log(typeof_.isDate(new Date())); // object
2. instanceof 不可以检测简单数据类型 null undefined 也不可以
let instanceof_ = {
isArray:(context)=> context instanceof Array ,
isObject:(context)=> context instanceof Object,
isString:(context)=> context instanceof String ,
isNumber:(context)=> context instanceof Number,
isBoolean:(context)=> context instanceof Boolean,
isFunction:(context)=> context instanceof Function,
isSymbol:(context)=> context instanceof Symbol,
isDate:(context)=> context instanceof Date,
}
console.log(instanceof_.isArray([])); // true
console.log(instanceof_.isObject({})); // true
console.log(instanceof_.isString("1111")); // false
console.log(instanceof_.isNumber(111)); // false
console.log(instanceof_.isBoolean(true)); // false
console.log(instanceof_.isFunction(new Function())); // true
console.log(instanceof_.isSymbol(Symbol())); // false
console.log(instanceof_.isDate(new Date())); // true
3. constructor null 与 undefined 没有**
let constructor_ = {
isArray:(context)=> context.constructor === Array ,
isObject:(context)=> context.constructor === Object,
isString:(context)=> context.constructor === String ,
isNumber:(context)=> context.constructor === Number,
isBoolean:(context)=> context.constructor === Boolean,
isFunction:(context)=> context.constructor === Function,
isSymbol:(context)=> context.constructor === Symbol,
isDate:(context)=> context.constructor === Date,
}
console.log(constructor_.isArray([])); // true
console.log(constructor_.isObject({})); // true
console.log(constructor_.isString("1111")); // true
console.log(constructor_.isNumber(111)); // true
console.log(constructor_.isBoolean(true)); // true
console.log(constructor_.isFunction(new Function())); // true
console.log(constructor_.isSymbol(Symbol())); // true
console.log(constructor_.isDate(new Date())); // true
4. toString 对象判断类型 toString Object 类型可以直接调用 toString() 其它需要用 call 或者 apply 来调用
let prototypeToString_ = {
isArray:(context)=>Object.prototype.toString.call(context)==="[object Array]",
isObject:(context)=>Object.prototype.toString.call(context)==="[object Object]",
isString:(context)=>Object.prototype.toString.call(context)==="[object String]",
isNull:(context)=>Object.prototype.toString.call(context)==="[object Null]",
isUndefined:(context)=>Object.prototype.toString.call(context)==="[object Undefined]",
isNumber:(context)=>Object.prototype.toString.call(context)==="[object Number]",
isBoolean:(context)=>Object.prototype.toString.call(context)==="[object Boolean]",
isFunction:(context)=>Object.prototype.toString.call(context)==="[object Function]",
isSymbol:(context)=>Object.prototype.toString.call(context)==="[object Symbol]",
isDate:(context)=>Object.prototype.toString.call(context)==="[object Date]",
}
console.log(prototypeToString_.isArray([])); // true
console.log(prototypeToString_.isObject({})); // true
console.log(prototypeToString_.isString("111")); // true
console.log(prototypeToString_.isNull(null)); // true
console.log(prototypeToString_.isUndefined(undefined)); // true
console.log(prototypeToString_.isNumber(11)); // true
console.log(prototypeToString_.isBoolean(true)); // true
console.log(prototypeToString_.isFunction(new Function())); // true
console.log(prototypeToString_.isSymbol(Symbol())); // true
console.log(prototypeToString_.isDate(new Date())); // true
