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High Performance JavaScript


Author: Nicholas C. Zakas

Publisher: O'Reilly Media


Publish Date: March 30, 2010

ISBN-10: 059680279X

Pages: 240

File Type: EPUB, MOBI

Language: English

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Book Preface

When JavaScript was first introduced as part of Netscape Navigator in 1996, performance wasn’t that important. The Internet was in its infancy and it was, in all ways, slow. From dial-up connections to underpowered home computers, surfing the Web was more often a lesson in patience than anything else. Users expected to wait for web pages to load, and when the page successfully loaded, it was a cause for celebration.

JavaScript’s original goal was to improve the user experience of web pages. Instead of going back to the server for simple tasks such as form validation, JavaScript allowed embedding of this functionality directly in the page. Doing so saved a rather long trip back to the server. Imagine the frustration of filling out a long form, submitting it, and then waiting 30–60 seconds just to get a message back indicating that you had filled in a single field incorrectly. JavaScript can rightfully be credited with saving early Internet users a lot of time.

The Internet Evolves

Over the decade that followed, computers and the Internet continued to evolve. To start, both got much faster. The rapid speed-up of microprocessors, the availability of cheap memory, and the appearance of fiber optic connections pushed the Internet into a new age. With high-speed connections more available than ever, web pages started becoming heavier, embedding more information and multimedia. The Web had changed from a fairly bland landscape of interlinked documents into one filled with different designs and interfaces. Everything changed, that is, except JavaScript.

What previously was used to save server roundtrips started to become more ubiquitous. Where there were once dozens of lines of JavaScript code were now hundreds, and eventually thousands. The introduction of Internet Explorer 4 and dynamic HTML (the ability to change aspects of the page without a reload) ensured that the amount of JavaScript on pages would only increase over time.

The last major step in the evolution of browsers was the introduction of the Document Object Model (DOM), a unified approach to dynamic HTML that was adopted by Internet Explorer 5, Netscape 6, and Opera. This was closely followed by the standardization of JavaScript into ECMA-262, third edition. With all browsers supporting the DOM and (more or less) the same version of JavaScript, a web application platform was born. Despite this huge leap forward, with a common API against which to write JavaScript, the JavaScript engines in charge of executing that code remained mostly unchanged.

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