毕业设计外文文献—什么是JavaScript.docxVIP

附录A 外文翻译—原文部分 Source: Professional JavaScript for Web Developers By: Nicholas C.Zakas What Is JavaScript? When JavaScript first appeared in 1995, its main purpose was to handle some of the input validation that had previously been left to server-side languages such as Perl. Prior to that time, a round-trip to the server was needed to determine if a required field had been left blank or an entered value was invalid. Netscape Navigator sought to change that with the introduction of JavaScript. The capability to handle some basic validation on the client was an exciting new feature at a time when use of telephone modems was widespread. The associated slow speeds turned every trip to the server into an exercise in patience. Since that time, JavaScript has grown into an important feature of every major web browser on the market. No longer bound to simple data validation, JavaScript now interacts with nearly all aspects of the browser window and its contents. JavaScript is recognized as a full programming language, capable of complex calculations and interactions, including closures, anonymous (lambda) functions, and even metaprogramming. JavaScript has become such an important part of the Web that even alternative browsers, including those on mobile phones and those designed for users with disabilities, support it. Even Microsoft, with its own client- side scripting language called VBScript, ended up including its own JavaScript implementation in Internet Explorer from its earliest version. The rise of JavaScript from a simple input validator to a powerful programming language could not have been predicted. JavaScript is at once a very simple and very complicated language that takes minutes to learn but years to master. To begin down the path to using JavaScripts full potential, it is important to understand its nature, history, and limitations. A SHORT HISTORY As the Web gained popularity, a gradual demand for client-side scripting languages developed. At the time, most