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1. Typeof operator
Example:
// 数值 typeof 37 === 'number'; // 字符串 typeof '' === 'string'; // 布尔值 typeof true === 'boolean'; // Symbols typeof Symbol() === 'symbol'; // Undefined typeof undefined === 'undefined'; // 对象 typeof {a: 1} === 'object'; typeof [1, 2, 4] === 'object'; // 下面的例子令人迷惑,非常危险,没有用处。避免使用它们。 typeof new Boolean(true) === 'object'; typeof new Number(1) === 'object'; typeof new String('abc') === 'object'; // 函数 typeof function() {} === 'function';
From the above example we can see that using typeof except array and null is judged as object Except for this, everything else can be judged normally.
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2. instanceof operator and constructor attribute of object
This operator is somewhat similar to object-oriented in JavaScript Relationship, to understand this, you must first understand object-oriented in JavaScript. Because this operator detects whether the prototype chain of the object points to the prototype object of the constructor.
Example:
3. Use Object.prototype.toString to determine whether it is a number
Object.prototype.toString.call( [] ) === '[object Array]' // true Object.prototype.toString.call( function(){} ) === '[object Function]' // true
Use call here Make this in toString point to obj. Then complete the judgment
4. Use the prototype chain to complete the judgment
[].__proto__ === Array.prototype // true var fun = function(){} fun.__proto__ === Function.prototype // true
5. Array.isArray()
Array.isArray([]) // true
ECMAScript5 officially introduces Array.isArray() into JavaScript for the purpose It is to accurately detect whether a value is an array. IE9, Firefox 4, Safari 5, Opera 10.5 and Chrome all implement this method. However, versions before IE8 are not supported.
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