JS中的类型识别

1 console.log(typeof("tom"));  //"string"
2 console.log(typeof(12)); //"number"
3 console.log(typeof(true)); //"boolean"
4 console.log(typeof(undefined)); //"undefined"
5 console.log(typeof(null)); //"objectl" null被识别为object
6 console.log(typeof({name:"yxz"})); //"object"
7 console.log(typeof(function(){})); // "function"

 1 function type(obj){
 2     return Object.prototype.toString.call(obj).slice(8,-1).toLowerCase();
 3 }
 4 console.log(type(1));//"number"
 5 console.log(type("abc"));//"string"
 6 console.log(type(true));//"boolean"
 7 console.log(type(undefined));//"undefined"
 8 console.log(type(null));//"null"
 9 console.log(type({}));//"object"
10 console.log(type(new Date));//"date"
11 console.log(type(function(){}));//"funciton"
12 console.log(type([]));//"array"
13 function Point(x,y){
14     this.x = x;
15     this.y = y;
16 }
17 console.log(type(new Point(1,2)));//"object" 自定义类型不能识别

 1 //标准类型
 2 console.log("tom".constructor == String);//true
 3 console.log((1).constructor == Number);//true
 4 console.log(true.constructor == Boolean);//true
 5 console.log({}.constructor == Object);//true
 6 //内置类型对象
 7 console.log([].constructor == Array);//true
 8 //自定义对象
 9 function Person(name){
10     this.name = name;
11 }
12 console.log(new Person("tom").constructor == Person);//true

 1 //识别内置对象类型
 2 console.log([] instanceof Array);//true
 3 //不能识别原始类型
 4 console.log(1 instanceof Number);//false
 5 console.log("tom" instanceof String);//false
 6 //能识别自定义对象类型及父子类型
 7 function Point(x,y){
 8     this.x = x;
 9     this.y = y;
10 }
11 function Circle(x,y,r){
12     Point.call(this,x,y);
13     this.radius = r;
14 }
15 Circle.prototype = new Point();
16 Circle.prototype.constructor = Circle;
17 var c = new Circle(1,1,2);
18 console.log(c instanceof Circle);//true
19 console.log(c instanceof Point);//true