js判断数据类型

标签：instanceof 判断 console log Object 数据类型 js toString var

ES5中，js中数据类型：number、string、boolean、undefined、null、object

js中获取数据类型常用的四种方式

实例：

var a = 123,
    b = true,
    c = "123",
    d = undefined,
    e = null;
var o = new Object();
var f = new Function();
var f1 = function(){};
function f2(){}
var arr = [];
var arr1 = new Array();
var reg = new RegExp();　　

1. typeof

 可以判断 js 中基本数据类型，但无法判断对象的具体类型 

console.log("a:"+typeof(a));
console.log("b:"+typeof(b));
console.log("c:"+typeof(c));
console.log("d:"+typeof(d));
console.log("e:"+typeof(e));
console.log("o:"+typeof(o));
console.log("f:"+typeof(f));
console.log("f1:"+typeof(f1));
console.log("f2:"+typeof(f2));
console.log("arr:"+typeof(arr));
console.log("arr1:"+typeof(arr1));
console.log("reg:"+typeof(reg));　　

注意：当使用基本包装类型创建字符串，数组或布尔值时，使用typeof返回的是Object

    判断基本类型

function ccTypeof(cc){
  return cc === null ? "null" : typrof(cc);
 }　　

2. Object.prototype.toString.call(1)

可以判断具体的对象类型，包括正则等，但是无法判断自定义对象类型。

console.log("a:"+ Object.prototype.toString.call(a));
console.log("b:"+ Object.prototype.toString.call(b));
console.log("c:"+ Object.prototype.toString.call(c));
console.log("d:"+ Object.prototype.toString.call(d));
console.log("e:"+ Object.prototype.toString.call(e));
console.log("o:"+ Object.prototype.toString.call(o));
console.log("f:"+ Object.prototype.toString.call(f));
console.log("f1:"+ Object.prototype.toString.call(f1));
console.log("f2:"+ Object.prototype.toString.call(f2));
console.log("arr:"+ Object.prototype.toString.call(arr));
console.log("arr1:"+ Object.prototype.toString.call(arr1));
console.log("reg:"+ Object.prototype.toString.call(reg)); 

function A(){
 this.a = 1;
}
var x = new A();
console.log(Object.prototype.toString.call(x)); 

3. instanceof

用法：变量 nstaceof 对象，返回值为boolean。

仅能判断对象的具体类型，但可以拥于判断自定义对象类型。

var a = 123,
    b = true,
    c = "123";
    //d = undefined,
    //e = null;
var o = new Object();
var f = new Function();
var f1 = function(){};
function f2(){}
var arr = [];
var arr1 = new Array();
var reg = new RegExp();

console.log(a instanceof Number);
console.log(b instanceof Boolean);
console.log(c instanceof String);
//console.log("d:"+d instanceof Undefined);
//console.log("e:"+e instanceof Null);
console.log(o instanceof Object);
console.log(f instanceof Function);
console.log(f1 instanceof Function);
console.log(f2 instanceof Function);
console.log(arr instanceof Array);
console.log(arr1 instanceof Array);
console.log(reg instanceof RegExp);　　

 

function A(){
 this.a = 1;
}
function B(){
 this.b = 2;
}
var x = new A();
if(x instanceof A){
  console.log("x is A");   
}
if(x instanceof B){
  console.log("x is B");   
}else{
  console.log("x is not B");  
}

4. constructor

查看对象对应的构造函数

object的每个实例都具有属性constructor，保存着用于创建当前对象的函数。

function A(){
 this.a = 1;
}

var x = new A();
console.log(x.constructor);

function A(){
 this.a = 1;
}
function B(){
 this.b = 2;
}
var x = new A();
if(x.constructor == A){
  console.log("x is A");   
}
if(x.constructor == B){
  console.log("x is B");   
}else{
  console.log("x is not B");  
}

但是Undefined和Null类型不能判断

 

打印所有类型

function ccTypeof(cc){
  var typeName == Object.prototype.toString.call(cc);
  if( typeName == "[object Object]"){
      typeName = "[object" + cc.constructor.name + "]";
   }
}

注意：判断数组还可以用数组的isArray()方法，语法：Array.isArray(arr)，返回值为Boolean值。

标签：instanceof,判断,console,log,Object,数据类型,js,toString,var
From： https://www.cnblogs.com/sexintercourse/p/16847326.html