js数据类型检测总结

<script>
  console.log(typeof(1));  //number
  console.log(typeof('hello'));  //string
  console.log(typeof(true));  //boolean
  console.log(typeof(undefined));  //undefined
  console.log(typeof(null));  //object
  console.log(typeof({}));  //object
  console.log(typeof(function() {}));  //function
</script>

<script>
  let arr = [1,2,3];
  let reg = /\w/;
  console.log(arr instanceof Array);  //true
  console.log(arr instanceof Object);  //true
  console.log(reg instanceof RegExp);  //true
  console.log(reg instanceof Object);  //true
</script>

<script>
  let num = 12;
  let obj = {};
  console.log(num.constructor == Number);//true
  console.log(obj.constructor == Object);//true
</script>

<script>
  1.constructor === Number;    //报错，Invalid or unexceped token
  (1).constructor === Number;    //true
  {}.constructor === Number;    //报错，Invalid or unexceped token
  ({}).constructor === Number;  //true
</script>

<script>
   function Fn() {};
  Fn.prototype = new Array;
  var f = new Fn;
  //f是一个函数，按道理说他的构造函数应该是Function,但是修改其原型链后，它的constructor变成了Array.
  console.log(f.constructor == Array);  //true
</script>

<script> 
  console.log(Object.prototype.toString.call(1));          //[object Number]
  console.log(Object.prototype.toString.call(/^sf/));        //[object RegExp]
  console.log(Object.prototype.toString.call("hello"));      //[object String]
  console.log(Object.prototype.toString.call(true));        //[object Boolean]
  console.log(Object.prototype.toString.call(null));        //[object Null]
  console.log(Object.prototype.toString.call(undefined));      //[object Undefined]
  console.log(Object.prototype.toString.call(function() {}));    //[object Function]
  console.log(typeof(Object.prototype.toString.call(function() {})));    //string
</script>