Tham khảo sách 'javascript bible_ chapter 25', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Navigator and Other Environment Objects JavaScript devotes one category of its objects to browser software also called the client by some users . These objects are not part of any windows or documents that you see but rather apply to the inner workings of the browser software. In addition to providing some of the same information that CGI programs on the server extract as environment variables these browser-level objects also include information about how well-equipped the browser is with regard to plug-ins and Java. And one object newly defined for Navigator 4 reveals information about the user s video monitor which may influence the way your scripts define information displayed on the page. The objects in this chapter don t show up on the JavaScript object hierarchy diagrams except as a freestanding group derived from the navigator and screen objects see Appendix A . Internet Explorer 4 s object model however places its corresponding objects under the window object. Because the window reference is optional you can omit it for Internet Explorer 4 and wind up with a crosscompatible script. With the added built-in capabilities that each generation of browser introduces these small independent objects are sure to grow even more in importance. Navigator Object In This Chapter Determining which browser the user has Branching scripts according to the user s operating system Verifying that a specific plug-in is installed 506 Part III JavaScript Object and Language Reference Properties Methods Event Handlers appName javaEnabled None appCodeName preference appVersion taintEnabled language mimeTypes platform plugins userAgent Syntax Accessing navigator object properties and methods method About this object In Chapter 14 I repeatedly mentioned that the window object is the top banana of the JavaScript object hierarchy. In other programming environments you will likely find an application level higher than the window. You may think that an object known as .
