什么是网页的性能?为什么网页性能比较重要?中间有哪些挑战和解决方案?本文从前端工程师的角度,列举了一些架构设计案例,介绍如何提高网站访问性能。比如:合理用力压缩技术,减小http请求数,cdn,延迟等等。

献良发布于2018/10/05

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1.Intro to Web Performance Ten Ways to a Faster Website Presented by: Sheila Eaton and Mohammad Durrani TechKnowFile, University of Toronto, May 5, 2016

2.Welcome! What is Web Performance? Why is it Important? Challenges and Solutions Questions and Further Reading Agenda

3.What is Web Performance ? Perceived Performance Optimized progressive rendering. Feels fast. Unoptimized Rendering Feels slow. developers.google.com /web/fundamentals/performance/critical-rendering-path /

4.Web Page Performance www.webpagetest.org /result/ 160504_ET_1A6P /1/details/

5.Why is Performance Important ? Puts users first Allows users to accomplish tasks in less than 2 seconds Respect for users builds trust Encourages return visits Reduce time and data costs for mobile users Accounts for international bandwidth Broaden access Small boost to search

6.Why Performance Matters www.akamai.com /us/en/web-and-mobile- performance.jsp 47% expect a web page to load in two seconds or less . 57% will abandon a page that takes 3 seconds or more to load 79% shoppers [students, faculty, donors ] who have trouble with web site performance say they won’t return to the site to buy again See Also: What does my site cost

7.Performance Challenges CHALLENGE 1: Number of HTTP Requests CHALLENGE 2 : Bigger File Sizes CHALLENGE 3 : Improving Perceived Perf . CHALLENGE 4: Latency

8.httparchive.org / trends.php Total Transfer Size & Total Requests

9.CHALLENGE 1: Number of HTTP Requests

10.40 requests Goal: Reduce number of requests How – some quick wins: Image svg sprites Remove Font Awesome and Google font Set one feature img each for news and events feeds Reduce size of banner Blur banner image and crop Reduce CSS* *For new USMC website (in progress) CSS is reduced by 36%

11.Why Reduce Requests A resource is requested Time is spent sending the request to the server and waiting for the server to respond Then downloading the response to add to webpage The less time it takes -- the better CHALLENGE 1: Number of HTTP Requests

12.Five Ways to Cope with Requests Resource Audit Image Sprites JS/CSS Concat Keep Alive Cache Static Files CHALLENGE 1 : Number of HTTP Requests

13.The fastest and best optimized resource is a resource not sent Ilya Grigorik , Google CHALLENGE 1: Number of HTTP Requests > Reducing Requests

14.Resource Audit Question everything: css/js/images/fonts/3rd-party CHALLENGE 1: Number of HTTP Requests > Reducing Requests Resource necessary? Value to user? More performant approach? Blocking page load? Place lower in markup? How is value tracked ?

15.Fonts P erformance costs of fonts? Aesthetic tradeoffs? CHALLENGE 1: Number of HTTP Requests > Reducing Requests Google Sans and Merriweather Bold, normal, italic Performance Hit 194 Arial and Times New Roman All weights No Performance Hit

16.Image Sprites Size of file is bigger but fewer http requests CHALLENGE 1: Number of HTTP Requests > Reducing Requests

17.CHALLENGE 1: Number of HTTP Requests > Reducing Requests JS/CSS Concat What is concat ? Combining like files to reduce the number of HTTP requests

18.CHALLENGE 1: Number of HTTP Requests > Reducing Requests JS/CSS Concat File1.js { //content file 1 } FileAll.js { //content file 1 //content file 2 //content file 3 } File2.js { // content file 2 } File3.js { // content file 3 }

19.CHALLENGE 1: Number of HTTP Requests > Reducing Requests Keep Alive http:// stackoverflow.com /questions/12550973/http-header-keep-alive-misunderstanding

20.CHALLENGE 1: Number of HTTP Requests > Reducing Requests Caching Static Files Assets don’t change often (css, images, js) Reduce number of requests by storing assets on client’s machine for a defined period of time Not spending time fetching resources Will only affect subsequent visits Test with webpagetest.org

21.CHALLENGE 2: Bigger File Sizes

22.Why Reduce Size of Resources Smaller the resource = the faster it will load Get files to the browser as fast as possible so it can start building the page CHALLENGE 2: Bigger File Sizes

23.Three Ways to Reduce File Sizes Images Right Size Right Format Compression Minification Gzip CHALLENGE 2: Bigger File Sizes

24.Image Compression Images count for just over 63% of page weight CHALLENGE 2: Bigger File Sizes > Reducing File Sizes > Images

25.Choosing the right file format CHALLENGE 2: Bigger File Sizes > Reducing File Sizes > Images

26.Serving the right size CHALLENGE 2: Bigger File Sizes > Reducing File Sizes > Images Don’t serve a 500x500 image intended as a 150x150 thumbnail

27.Image Compression Caveat: Strips meta data CHALLENGE 2: Bigger File Sizes > Reducing File Sizes > Images Lossless compression allows original image to be perfectly reconstructed from compressed data. Lossy compression reconstructs an approximation of original data

28.Image Compression CHALLENGE 2: Bigger File Sizes > Reducing File Sizes > Images 69% savings (right) in compressed png. No perceptual difference in quality . tinypng.com /

29.Image Compression CHALLENGE 2: Bigger File Sizes > Reducing File Sizes > Images Tools Popular web tools Plugins for wp / drupal Task runners

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