How to determine whether an object is an array (function) in js

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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