js中类型判断

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JS判断数据类型

js基本类型有 Undefined、Null、Boolean、Number和String,Object（由名值对集合）

typeof判断类型

   var nullValue = null,boolValue = true，nmValue=12,strValue = 'test';   var objValue={x:y},arrayValue = [1,23,3],   functionValue = function(){       console.info('function')   };   typeof nullValue == 'object';//true   typeof boolValue == 'boolean';//true   typeof nmValue == 'number';//true   typeof strValue  == 'string';//true   typeof objValue== 'object';//true   typeof unValue== 'undefined';//true   typeof arrayValue == 'object';//true   typeof functionValue == 'function';//true   typeof NaN//"number"   /*   *typeof 只能准确判断Undefined、Boolean、Number和String类型和function   *对Null，Object,Array测试其值为'object'   **/

instanceof判断

instanceof 判断已知对象，主要用于判断Array,object等

  [1,2]  instanceof Array;//true 数组  new Date() instanceof Date;//Data  var Obj = function(){}  Obj.prototype.info = function(){    console.info(Array.prototype.slice.apply(argument,[1]))  }  var testObj = new Obj();  testObj instanceof Obj;//true  自定义对象  var fucObj = function(){};  fucObj  instanceof Function;//true 函数判断  /*  *instanceof 适合对象判断  **/

constructor判断

适用于对象的判断

   false.constructor === Boolean;//true   'test'.constructor === String;//true   [1,23].constructor === Array;//true     var obj = {x:1}   obj .constructor === Object;//true  var funtest = function(){}  funtest .constructor === Function;//true  new Date().constructor  === Date;//true  //对于继承  var A = function(){};  var B = function(){};  A.prototype = new B();  var a = new A();  a.constructor === B;//true  a.constructor === A;//false  /*  *此处对于instanceof 能胜任判断  **/

Object.prototype.toString.apply()判断

  "[Object Array]" === Object.prototype.toString.apply([]);//true  "[object Object]"=== Object.prototype.toString.apply({});//true  "[object String]" === Object.prototype.toString.apply('123');//true  "[object Number]" === Object.prototype.toString.apply(123);//true  "[object Boolean]" === Object.prototype.toString.apply(false);//true  "[object Date]" === Object.prototype.toString.apply(new Date());//  "[object Null]" === Object.prototype.toString.apply(null);//true  "[object Undefined]" ===  Object.prototype.toString.apply(undefined);//true

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