Why Does `typeof` Return \'Object\' for JavaScript Arrays?

Understanding Array Type in JavaScript: Why Does typeof Return "Object" Instead of "Array"?

JavaScript exhibits an intriguing behavior where the typeof operator returns "object" for an array of objects. This can be observed in scenarios such as the following code:

$.ajax({
  url: 'http://api.twitter.com/1/statuses/user_timeline.json',
  data: { screen_name: 'mick__romney' },
  dataType: 'jsonp',
  success: function (data) {
    console.dir(data); // Array[20]
    alert(typeof data); // Object
  },
});

In the above code, data is an array of objects representing Twitter statuses. While console.dir() reports that the type is "Array", typeof returns "Object".

This behavior stems from the fact that JavaScript Arrays are technically objects. They inherit from the Object prototype, which means that they possess object-like properties and methods. This inheritance is responsible for the "Object" result from typeof.

To determine if a variable is truly an array in JavaScript, there are several reliable methods:

1. instanceof Operator:

var isArr = data instanceof Array;

2. Array.isArray() Method:

var isArr = Array.isArray(data);

3. Object.prototype.toString.call() Method:

isArr = Object.prototype.toString.call(data) == '[object Array]';

4. jQuery isArray() Function (if using jQuery):

var isArr = $.isArray(data);

These methods offer more accurate results than typeof when distinguishing between arrays and other types of objects. By leveraging these alternatives, developers can confidently work with arrays in JavaScript without the confusion caused by the typeof behavior.

The above is the detailed content of Why Does `typeof` Return \'Object\' for JavaScript Arrays?. For more information, please follow other related articles on the PHP Chinese website!