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]