外文翻譯--javascript的權(quán)威指南

1、1外文原文JavaScript The Definitive GuideJavaScript is the programming language of the Web. The overwhelming majority of modern websites use JavaScript, and all modern web browsers—on desktops, game consoles ,tablets, and sma

2、rt phones—include JavaScript interpreters, making JavaScript the most ubiquitous programming language in history. JavaScript is part of the triad of technologies that all Web developers must learn: HTML to specify the co

3、ntent of web pages ,CSS to specify the presentation of web pages ,and JavaScript to specify the behavior of web pages.If you are already familiar with other programming languages,it may help you to know that JavaScript i

4、s a high-level,dynamic,untyped interpreted programming language that is well-suited to object-oriented and functional programming styles. JavaScript derives its syntax from Java,its first-class functions from Scheme,and

5、its prototype-based inheritance from Self.But you do not need to know any of those languages,or be familiar with those terms,to use this book and learn JavaScript.The name ‘JavaScript’is actually somewhat misleading.Exce

6、pt for a superficial syntacticresemblance, JavaScript is completely different from the Java programming language.And JavaScript has long since outgrown its scripting-language roots to become a robust and efficient genera

7、l-purpose language.The latest version of the language(see the sidebar)defines new features for serious large-scale software development.Lexical Structure The lexical structure of a programming language is the set of elem

8、entary rules that specifies how you write program in that language.It is the lowest-level syntax of a language;it specifies such things as what variable names look like,the delimiter characters for comments,and how one p

9、rogram statement is separated from the next.This short chapter documents the lexical structure of JavaScript.Types，Values，and VariablesComputer programs work by manipulating values, such as the number 3.14 or the text “H

10、ello World.”The kinds of values that can be represented and manipulated in a 3true ,false, null, thisWe learned about true, false, and null. Unlike the other keywords, this is not a constant—it evaluates to different val

11、ues in different places in the program. The this keyword is used in object-oriented programming. Within the body of a method, this evaluates to the object on which the method was invoked.When any identifier appears by i

12、tself in a program, JavaScript assumes it is a variable and looks up its value. If no variable with that name exists, the exception evaluates to the undefined value. In the strict mode if ECMAScript5 , however ,an attemp

13、t to evaluate a nonexistent variable throws a ReferenceError instead. The Java programming language and platform have emerged as major technologies for performing e-business functions. Java programming standards have ena

14、bleedportability of applications andthe reuse of application components across computing platforms. Sun Microsystems' Java Community Process continues to be a strong base for the growth of the Java infrastructur-e an

15、d language standards. This growth of open standards creates new opportunities for designers and developers of applications and services . Applications of Java Javauses many familiar programming concepts andconstructs an

16、d allows portability by providing a common interface through an external Java Virtual Machine (JVM). A virtual machine is a self-contained operating environment, created by a software layer that behaves as if it were a s

17、eparate computer. Benefits of creating virtualmachines include better exploitation of powerful computing resources and isolation of applications to prevent cross-corruption and improve security.The JVM allows computing

18、devices with limited processors or memory to handle more advanced applications by calling up software instructions inside theJVM to perform most of the work. This also reduces the size and complexity of Java applications

19、 because many of the core functions and processing instructions were built into the JVM. As a result, software same application for every operating system.Java also provides security by instructing the application to int

20、eract with the virtual machine, which served as a barrier between applications and the core system, effectively protecting systems from malicious code. Among other things, Java is tailor-made for the growing Internet bec