tailieunhanh - Javascript bible_ Chapter 31

Tham khảo sách 'javascript bible_ chapter 31', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Control Structures CHAPTER 3 1 You get up in the morning go about your day s business and then turn out the lights at night. That s not much different from what a program does from the time it starts to the time it ends. But along the way both you and a program take lots of tiny steps not all of which advance the processing in a straight line. At times you have to control what s going on by making a decision or repeating tasks until the whole job is finished. Control structures are the facilities that make these tasks possible in JavaScript. JavaScript control structures follow along the same lines of many programming languages particularly with additions made in Navigator 4 and Internet Explorer 4 for JavaScript . Basic decision-making and looping constructions satisfy the needs of just about all programming tasks. If and If. . .Else Decisions In This Chapter How to branch script execution down multiple paths Looping through ordered collections of data How to use labels to assist in script navigation Nav2 Nav3 Nav4 IE3 J1 IE3 J2 IE4 J3 Compatibility JavaScript programs frequently have to make decisions based on the current values of variables or object properties. Such decisions can have only two possible outcomes at a time. The factor that determines the path the program takes at these decision points is the truth of some statement. For example when you enter a room of your home at night the statement under test is something like It is too dark to see without a light. If that statement is true you switch on the light if that statement is false you carry on with your primary task. Simple decisions JavaScript syntax for this kind of simple decision always begins with the keyword if followed by the condition to test and then the statements that execute if the condition yields a 646 Part III JavaScript Object and Language Reference true result. JavaScript uses no then keyword as some other languages do the keyword is implied by the way the various components of .