转贴:https://10up.github.io/Engineering-Best-Practices/javascript/#performance

Performance

Writing performant code is absolutely critical. Poorly written JavaScript can significantly slow down and even crash the browser. On mobile devices, it can prematurely drain batteries and contribute to data overages. Performance at the browser level is a major part of user experience which is part of the 10up mission statement.

Only Load Libraries You Need

JavaScript libraries should only be loaded on the page when needed. jquery-1.11.1.min.js is 96 KB. This isn't a huge deal on desktop but can add up quickly on mobile when we start adding a bunch of libraries. Loading a large number of libraries also increases the chance of conflictions.

Use jQuery Wisely

jQuery is a JavaScript framework that allows us easily accomplish complex tasks such as AJAX and animations. jQuery is great for certain situations but overkill for others. For example, let's say we want to hide an element:

document.getElementById( 'element' ).style.display = 'none';

vs.

jQuery( '#element' ).hide();

The non-jQuery version is much faster and is still only one line of code.

Try to Pass an HTMLElement or HTMLCollection to jQuery Instead of a Selection String

When we create a new jQuery object by passing it a selection string, jQuery uses it's selection engine to select those element(s) in the DOM:

jQuery( '#menu' );

We can pass our own HTMLCollection or HTMLElement to jQuery to create the same object. Since jQuery does a lot of magic behind the scenes on each selection, this will be faster:

jQuery( document.getElementById( 'menu' ) );

Cache DOM Selections

It's a common JavaScript mistake to reselect something unnecessarily. For example, every time a menu button is clicked, we do not need to reselect the menu. Rather, we select the menu once and cache it's selector. This applies whether you are using jQuery or not. For example:

non-jQuery Uncached:

var hideButton = document.getElementsByClassName( 'hide-button' )[0];
hideButton.onclick = function() {
var menu = document.getElementById( 'menu' );
menu.style.display = 'none';
}

non-jQuery Cached:

var menu = document.getElementById( 'menu' );
var hideButton = document.getElementsByClassName( 'hide-button' )[0];
hideButton.onclick = function() {
menu.style.display = 'none';
}

jQuery Uncached:

var $hideButton = jQuery( '.hide-button' );
$hideButton.on( 'click', function() {
var $menu = jQuery( '#menu' );
$menu.hide();
});

jQuery Cached:

var $menu = jQuery( '#menu' );
var $hideButton = jQuery( '.hide-button' );
$hideButton.on( 'click', function() {
$menu.hide();
});

Notice how in cached versions we are pulling the menu selection out of the event handler so it only happens once. Non-jQuery cached is not surprisingly the fastest way to handle this situation.

Event Delegation

Event delegation is the act of adding one event listener to a parent node to listen for events bubbling up from children. This is much more performant than adding one event listener for each child element. Here is an example:

Without jQuery:

document.getElementById( 'menu' ).addEventListener( 'click', function( event ) {
if( event.target && event.target.nodeName === 'LI' ) {
// Do stuff!
}
});

With jQuery:

jQuery( '#menu' ).on( 'click', 'li', function() {
// Do stuff!
});

The non-jQuery method is as usual more performant. You may be wondering why we don't just add one listener to <body> for all our events. Well, we want the event to bubble up the DOM as little as possible for performance reasons. This would also be pretty messy code to write.

Design Patterns back to top

Standardizing the way we structure our JavaScript allows us to collaborate more effectively with one another. Using intelligent design patterns improves maintainability, code readability, and even helps to prevent bugs.

Don't Pollute the Window Object

Adding methods or properties to the window object or the global namespace should be done carefully. window object pollution can result in collisions with other scripts. We should wrap our scripts in closures and expose methods and properties to window decisively.

When a script is not wrapped in a closure, the current context or this is actuallywindow:

window.console.log( this === window ); // true
for ( var i = 0; i < 9; i++ ) {
// Do stuff
}
var result = true;
window.console.log( window.result === result ); // true
window.console.log( window.i === i ); // true

When we put our code inside a closure, our variables are private to that closure unless we expose them:

( function() {
for ( var i = 0; i < 9; i++ ) {
// Do stuff
} window.result = true;
})(); window.console.log( typeof window.result !== 'undefined' ); // true
window.console.log( typeof window.i !== 'undefined' ); // false

Notice how i was not exposed to the window object.

Use Modern Functions, Methods, and Properties

It's important we use language features that are intended to be used. This means not using deprecated functions, methods, or properties. Whether we are using a JavaScript or a library such as jQuery or Underscore, we should not use deprecated features. Using deprecated features can have negative effects on performance, security, maintainability, and compatibility.

For example, in jQuery jQuery.live() is a deprecated method:

jQuery( '.menu' ).live( 'click', function() {
// Clicked!
});

We should use jQuery.on() instead:

jQuery( '.menu' ).on( 'click', function() {
// Clicked!
});

Another example in JavaScript is escape() and unescape(). These functions were deprecated. Instead we should use encodeURI()encodeURIComponent(),decodeURI(), and decodeURIComponent().

Code Style & Documentation back to top

We conform to WordPress JavaScript coding standards.

In the absence of an adopted core standard for JavaScript documentation, we follow the JSDoc3 standards.

Unit and Integration Testing back to top

At 10up, we generally employ unit and integration tests only when building applications that are meant to be distributed. Writing tests for client themes usually does not offer a huge amount of value (there are of course exceptions to this). When we do write tests, we use QUnit which is a WordPress standard.

Libraries back to top

There are many JavaScript libraries available today. Many of them directly compete with each other. We try to stay consistent with what WordPress uses. The following is a list of primary libraries used by 10up.

DOM Manipulation

jQuery - Our and WordPress's library of choice for DOM manipulation.

Utility

Underscore - Provides a number of useful utility functions such as clone(),each(), and extend(). WordPress core uses this library quite a bit.

Frameworks

Backbone - Provides a framework for building complex JavaScript applications. Backbone is based on the usage of models, views, and collections. WordPress core relies heavily on Backbone especially in the media library. Backbone requires Underscore and a DOM manipulation library (jQuery)

Performance js的更多相关文章

  1. You Don't Know JS: Scope & Closures(翻译)

    Chapter 1: What is Scope? 第一章:什么是作用域 One of the most fundamental paradigms of nearly all programming ...

  2. iOS-监听原生H5性能数据window.performance

    WebKit-WKWebView iOS8开始苹果推荐使用WKWebview作为H5开发的核心组件,以替代原有的UIWebView,以下是webkit基本介绍介绍: 介绍博客 Webkit H5 - ...

  3. 页面性能监控之performance

    页面性能监测之performance author: @TiffanysBear 最近,需要对业务上的一些性能做一些优化,比如降低首屏时间.减少核心按钮可操作时间等的一些操作:在这之前,需要建立的就是 ...

  4. Performance --- 前端性能监控

    阅读目录 一:什么是Performance? 二:使用 performance.timing 来计算值 三:前端性能如何优化? 四:Performance中方法 五:使用performane编写小工具 ...

  5. 基于HTML5实现3D热图Heatmap应用

    Heatmap热图通过众多数据点信息,汇聚成直观可视化颜色效果,热图已广泛被应用于气象预报.医疗成像.机房温度监控等行业,甚至应用于竞技体育领域的数据分析. http://www.hightopo.c ...

  6. 基于HTML5实现的Heatmap热图3D应用

    Heatmap热图通过众多数据点信息,汇聚成直观可视化颜色效果,热图已广泛被应用于气象预报.医疗成像.机房温度监控等行业,甚至应用于竞技体育领域的数据分析. 已有众多文章分享了生成Heatmap热图原 ...

  7. drupal笔记

    $app_root :网站根目录 安装 汉化:1将汉化包放置drupal8\sites\default\files\translations下安装:2极简版的话需要在extend(扩展)中安装Inte ...

  8. [React] 10 - Tutorial: router

    Ref: REACT JS TUTORIAL #6 - React Router & Intro to Single Page Apps with React JS Ref: REACT JS ...

  9. 测开之路七十六:性能测试蓝图之html

    <!-- 继承base模板 -->{% extends 'base.html' %} {% block script %} <!-- 从cdn引入ace edter的js --> ...

随机推荐

  1. dijstra算法,求源点到各个顶点的最短距离

    1:dijstra算法常用语求最短距离, dijstra每次从未发现节点n[]中,发现距离源点最短的节点m,求出最短节点后,将m添加到已发现节点y[]中,用该节点m进行更新其它未发现节点n[]-m的最 ...

  2. 通过交换a,b 中的元素,使[序列a 元素的和]与[序列b 元素的和]之间的差最小

    题目描述: 有两个序列a,b,大小都为n,序列元素的值任意整数,无序:要求:通过交换a,b 中的元素,使[序列a 元素的和]与[序列b 元素的和]之间的差最小.例如:var a=[100,99,98, ...

  3. Mysql—(1)—

    sql语句 sql是Structured Query Language(结构化查询语言)的缩写.SQL是专为数据库而建立的操作命令集,是一种功能齐全的数据库语言. 在使用它时,只需要发出“做什么”的命 ...

  4. iOS 关于BTC 一些知识点

    1.BTC 用这个网 可以校验 自己的库生成的助记词 地址 是否是合法正常的 https://iancoleman.io/bip39/ 2.知晓 BTC 钱包是否有钱 和交易记录 https://te ...

  5. 带你走进ajax(2)

    ajax原理介绍 传统的web应用 传统的web应用是客户端向服务器发送一个http请求后,客户端要一直等待服务器的响应,这时用户什么事也干不成. 最麻烦的是对于表单的提交.比如用户要填写用户信息,等 ...

  6. 走近AbstractQueuedSynchronizer

    走近AbstractQueuedSynchronizer 一.从类结构开始 Java并发包中的同步器是很多并发组件的基础,如各种Lock,ConcurrentHashMap中的Segment,阻塞队列 ...

  7. Oracle中的substr()函数详解案例

    1)substr函数格式   (俗称:字符截取函数) 格式1: substr(string string, int a, int b); 格式2:substr(string string, int a ...

  8. iOS开发之plist文件操作

    之前在想用代码去实现很多界面上能用interface builder可以拖进去的功能,现在想想真是够无知的啊.不仅效率低下,而且对于代码的维护带来不少麻烦,这段时间一直在反思看了design+code ...

  9. 基于Node.js的爬虫工具 – Node Crawler

    Node Crawler的目标是成为最好的node.js爬虫工具,目前已经停止维护. 我们来抓取光合新知博客tech栏目中的文章信息.访问http://dev.guanghe.tv/category/ ...

  10. Maven取消编译自动测试

    Maven取消编译自动测试 <build> <plugins> <plugin> <groupId>org.apache.maven.plugins&l ...