Tham khảo sách 'javascript bible_ chapter 13', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | JavaScript Essentials The purpose of most JavaScript scripts is to make a Web page interactive whether or not a program is running on the server to enhance that interactivity. Making a page interactive means tracking user action and responding with some visible change on the page. The avenues for communication between user and script include familiar onscreen elements such as fields and buttons as well as dynamic content in level 4 browsers. To assist the scripter in working with these elements the browser and JavaScript implements them as software objects. These objects have properties that often define the visual appearance of the object. Objects also have methods which are the actions or commands that an object can carry out. Finally these objects have event handlers that trigger the scripts you write in response to an action in the document usually instigated by the user . This chapter begins by helping you understand that the realm of possibilities for each JavaScript object is the key to knowing how you can use JavaScript to convert an idea into a useful Web page. From there you see how to add scripts to an HTML page and learn several techniques to develop applications for a wide range of browsers including nonscriptable browsers. Language and Document Objects As described briefly in Chapter 2 the environment you will come to know as JavaScript scripting is composed of two quite separate pieces the core JavaScript language and the document object models of things you script with the language. By separating the core language from the objects it works with the language s designers created a programming language that can be linked to a variety of object collections for different environments. In fact even within Web applications the same core JavaScript language is applied to the browser document object model and the server-side object model for processing requests and communicating with databases. Everything an author knows about the core language can be .
