How to detect custom global variables in JavaScript

Source: Internet
Author: User
Tags mootools

Translator Note: The misuse of global variables is a very bad programming. It is easy to cause dependency and state confusion. In the language of automatic garbage collection, Java and JavaScript, the global (visible) variable has been a hidden killer of memory leaks.

This paper provides a reliable way to implement the global variable detection.

It is not a good practice to arbitrarily set global variables in JavaScript. The original author participated in the MooTools project, which, according to him, had been heard every day for about 10 years. MooTools extends the native JS object of the browser, but also uses some global variables, such as Browser and $$ . I think "global variables are too scary!" (Original global VARs is terrible) ", somewhat helpless, jQuery and JavaScript loaders all use at least one global variable.

In addition to intentional global variables, it is a bad habit to leak an object to the global space, which is usually the rotten code. So how do we detect which global variables we put in ourselves? Understand the principle code is very simple:

// 创建一个新的  iframe, 然后将其 `contentWindow` 中的属性值// 与当前 window 中的属性值对比, 不在其中的就是自定义对象(function() {    var iframe = document.createElement(‘iframe‘);    iframe.onload = function() {        // 使用 Object.keys() 获取对象的所有属性名         var iframeKeys = Object.keys(iframe.contentWindow);        Object.keys(window).forEach(function(key) {            // 如果存在 window 中,而 iframe 中却没有            if(!(key in iframeKeys)) {                // 输出到控制台,也可以加入数组,自己处理                console && console.log && console.log(key);            }        });    };    // 必须在 设置 src 属性之前添加 onload 事件。    // 在 onload 里面 contentWindow 才变得可用!     iframe.src = ‘about:blank‘;    document.body.appendChild(iframe);})();

Of course, because it is 2 window objects, it is also 2 different document, so you will see,, window document top , and location both are output. But the rest is intentionally or unintentionally leaked to the global space by JavaScript code.

Original link: Get Global Variables with JavaScript

Original date: August 31, 2015

Translation Date: September 10, 2015

Translators: Anchor Http://

How to detect custom global variables in JavaScript

Related Article

E-Commerce Solutions

Leverage the same tools powering the Alibaba Ecosystem

Learn more >

Apsara Conference 2019

The Rise of Data Intelligence, September 25th - 27th, Hangzhou, China

Learn more >

Alibaba Cloud Free Trial

Learn and experience the power of Alibaba Cloud with a free trial worth $300-1200 USD

Learn more >

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: and provide relevant evidence. A staff member will contact you within 5 working days.