JavaScript has a bad reputation that isnt entirely deserved It began as a

Javascript has a bad reputation that isnt entirely

This preview shows page 206 - 208 out of 517 pages.

JavaScript has a bad reputation that isn’t entirely deserved. It began as a language that would allow Web browsers to run simple client-side code to validate form inputs, animate page elements, or communicate with Java applets. Inexperienced programmers began to copy-and-paste simple JavaScript examples to achieve appealing visual effects, albeit with terrible programming practices, giving the language itself a bad reputation. In fact, JavaScript is a powerful and expressive language that incorporates great ideas enabling reuse and DRYness, such as closures and higher-order functions, but people without programming experience rarely use these tools properly. That said, because of JavaScript’s turbulent birth, its syntax and semantics have quirks ranging from the idiosyncratic to the regrettable, with almost as many special-case exceptions as there are rules. In addition, there are incompatibilities among different versions of the JavaScript interpreter and across different browsers’ JavaScript Application Programming Interface (JSAPI), the browser functionality that lets JavaScript code manipulate the content of the current HTML page. We will avoid compatibility problems in two major ways: quirksmode.org tells you more about JSAPI browser incompatibilities than you want to know. 1. Restricting ourselves to language features in the ECMAScript 3 standard, which all browsers support 2. Using the powerful jQuery library, rather than individual browsers’ JSAPIs, to interact with HTML documents Section 6.2 introduces the language and how code is connected to Web pages and Section 6.3 describes how its functions work, an understanding of which is the basis of writing clean and unobtrusive JavaScript code. Section 6.4 introduces jQuery , which overlays the separate browsers’ incompatible JSAPIs with a single API that works across all browsers, and Section 6.5 describes how jQuery’s features make it easy to program interactions between page elements and JavaScript code. jQuery can be viewed as an enhanced Adapter (Section 11.6 ) to the various browsers’ JSAPIs. Section 6.6 introduces AJAX programming. In 1998, Internet Explorer 5 introduced a new mechanism that allowed JavaScript code to communicate with a SaaS server after a page had been loaded, and use information from the server to update the page “in place” without the user having to reload a new page. Other browsers quickly copied the technology. Developer Jesse James Garrett coined the term AJAX , for Asynchronous JavaScript And XML, to describe how the combination of this technology to power impressive “Web 2.0” apps like Google Maps. Ironically, modern AJAX programming involves much less XML than originally, as we’ll see.
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Testing client-side JavaScript is challenging because browsers will fail silently when an error occurs rather than displaying JavaScript error messages to unsuspecting users. Fortunately, the Jasmine TDD framework will help you test your code, as Section 6.7 describes.
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  • Spring '19
  • Dr.Marcos

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