typeof

对检测 null、object、array 都是返回 object

  1. console.log(typeof null); // object
  2. console.log(typeof []); // object
  3. console.log(typeof {}); // object
  4. console.log(typeof new Number(1)); // object

instanceof

判断对象是否是指定构造函数的实例，无法判断原始值

  1. console.log([] instanceof Array); // true
  2. console.log({} instanceof Array); // true
  3. console.log(function() {} instanceof Function); // true
  5. console.log(1 instanceof Number); // false
  6. console.log(new Number(1) instanceof Number); // true

toString

什么类型都可以，只是慢

  1. function myTypeof(target) {
  2.   var temp = {
  3.       '[object Object]': 'object',
  4.     '[object Array]': 'array',
  5.     '[object Number]': 'obj-number',
  6.     '[object Boolean]': 'obj-boolean',
  7.     '[object String]': 'obj-string'
  8.   }
  11.     if(target === null) {
  12.       return 'null';
  13.   } else if(typeof target === 'object') {
  14.       retrun temp[Object.prototype.toString.call(target)];
  15.   } else {
  16.       return typeof target;
  17.   }
  18. }
  20. console.log(myTypeof(null)); // null
  21. console.log(myTypeof(undefined)); // undefined
  22. console.log(myTypeof(false)); // boolean
  23. console.log(myTypeof(1)); // number
  24. console.log(myTypeof(new Number(1))); // obj-number
  25. console.log(myTypeof(function() {})); // function
  26. console.log(myTypeof([]); // array
  27. console.log(myTypeof({}); // object

Array.prototype.isArray

ES5 新增，检查是否为数组最快的方法

  1. console.log(Array.isArray(null)); // false
  2. console.log(Array.isArray(undefined)); // false
  3. console.log(Array.isArray(false)); // false
  4. console.log(Array.isArray(1)); // false
  5. console.log(Array.isArray(new Number(1))); // false
  6. console.log(Array.isArray(function() {})); // false
  7. console.log(Array.isArray([]); // true
  8. console.log(Array.isArray({}); // false