JS中检测数据类型的几种方式及优缺点小结

console.log([] instanceof Array);//->true
console.log(/^$/ instanceof RegExp);//->true
console.log([] instanceof Object);//->true
console.log([].constructor === Array);//->true
console.log([].constructor === Object);//->false
constructor可以避免instanceof检测数组的时候,用Object也是true的问题
console.log({}.constructor === Object);//true<br>console.log([].constructor === Object);//false

var oDiv = document.getElementById("div1");
//HTMLDivElement->HTMLElement->Element->Node->EventTarget->Object
console.log(oDiv instanceof HTMLDivElement);//->true
console.log(oDiv instanceof Node);//->true
console.log(oDiv instanceof Object);//->true　　

console.log(1 instanceof Number);//->false

var ary = [];
var ary = new Array;

var num1 = 1;
var num2 = new Number("1");
console.log(typeof num1,typeof num2);//->"number" "object"　

function Fn() {}
var f = new Fn;
console.log(f instanceof Array);//->false f不是一个数组,它就是一个普通的实例(普通的对象)

function Fn() {
}
Fn.prototype = new Array;//->Fn子类继承了Array这个父类中的属性和方法
var f = new Fn;
console.log(f instanceof Array);//->true

var oDiv = document.getElementById("div1");
oDiv.toString(); //->调用的其实也是Object.prototype.toString...
//alert、document.write 这两种输出的方式其实都是把要输出的内容先转换为字符串,然后再输出的<br>
alert([]); //->""
alert(true); //->"true"
alert({}); //->这个就要调用Object.prototype上的toString了 ->"[object Object]"
//定义toString变量是为了简便书写，同时降低作用域链检索的性能损耗
var toString = Object.prototype.toString;
console.log(toString.call(1));//[object Number]
console.log(toString.call(undefined));//[object Undefined]
console.log(toString.call(null));//[object Null]
console.log(toString.call(false));//[object Boolean]
console.log(toString.call("s"));//[object String]
console.log(toString.call({}));//[object Object]
console.log(toString.call(/[a]/g));//[object RegExp]
console.log(toString.call(function(){}));//[object Function]

var dataType = {
    '[object Null]' : 'null',
    '[object Undefined]' : 'undefiend',
    '[object Boolean]' : 'boolean',
    '[object Number]' : 'number',
    '[object String]' : 'string',
    '[object Function]' : 'function',
    '[object Array]' : 'array',
    '[object Date]' : 'date',
    '[object RegExp]' : 'regexp',
    '[object Object]' : 'object',
    '[object Error]' : 'error'
  },
  toString = Object.prototype.toString;
function type(obj) {
  return dataType[toString.call(obj)];
}
//生成is系列函数
function createValidType() {
  for(var p in dataType) {
    var objType = p.slice(8, -1);
    (function(objType) {
      window['is' + objType] = function(obj) {
        return type(obj) === objType.toLowerCase();
      }
    })(objType)
  }
}
createValidType();
console.log(isObject({}));//true
console.log(isDate(new Date()));//true
console.log(isBoolean(false));//true
console.log(isString(1));//false
console.log(isError(1));//false
console.log(isError(new Error()));//true
console.log(isArray([]));//true
console.log(isArray(1));//false

console.log(type({}));//"object"
console.log(type(new Date()));//"date"
console.log(type(false));//"boolean"
console.log(type(1));//"number"
console.log(type(1));//"number"
console.log(type(new Error()));//"error"
console.log(type([]));//"array"
console.log(type(1));//"number"