typeof操作符，返回数据类型Array.isArray()、Object.prototype.toString.call()

源地址https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Operators/typeof

typeof操作符

 // Numbers
 typeof 37 === 'number';
 typeof 3.14 === 'number';
 typeof Math.LN2 === 'number';
 typeof Infinity === 'number';
 typeof NaN === 'number'; // 尽管NaN是"Not-A-Number"的缩写
 typeof Number(1) === 'number'; // 但不要使用这种形式!

 // Strings
 typeof "" === 'string';
 typeof "bla" === 'string';
 typeof (typeof 1) === 'string'; // typeof总是返回一个字符串
 typeof String("abc") === 'string'; // 但不要使用这种形式!

 // Booleans
 typeof true === 'boolean';
 typeof false === 'boolean';
 typeof Boolean(true) === 'boolean'; // 但不要使用这种形式!

 // Symbols
 typeof Symbol() === 'symbol';
 typeof Symbol('foo') === 'symbol';
 typeof Symbol.iterator === 'symbol';

 // Undefined
 typeof undefined === 'undefined';
 typeof declaredButUndefinedVariable === 'undefined';
 typeof undeclaredVariable === 'undefined';

 // Objects
 typeof {a:1} === 'object';

 // 使用Array.isArray 或者 Object.prototype.toString.call
 // 区分数组,普通对象
 typeof [1, 2, 4] === 'object';

 typeof new Date() === 'object';

Array.isArray()判断是否为数组

 var ar = [];
 var result = Array.isArray(ar);
 // Output: true

 var ar = new Array();
 var result = Array.isArray(ar);
 // Output: true

 var ar = [1, 2, 3];
 var result = Array.isArray(ar);
 // Output: true

 var result = Array.isArray("an array");
 document.write(result);
 // Output: false

Object.prototype.toString.call()精准判断数据类型

 console.log(Object.prototype.toString.call(123)) //[object Number]
 console.log(Object.prototype.toString.call('123')) //[object String]
 console.log(Object.prototype.toString.call(undefined)) //[object Undefined]
 console.log(Object.prototype.toString.call(true)) //[object Boolean]
 console.log(Object.prototype.toString.call({})) //[object Object]
 console.log(Object.prototype.toString.call([])) //[object Array]
 console.log(Object.prototype.toString.call(function(){})) //[object Function]