Javascript Loops

3 Key excerpts on "Javascript Loops"

• 

  eBook - ePub

  JavaScript from Beginner to Professional

  Learn JavaScript quickly by building fun, interactive, and dynamic web apps, games, and pages

  • Laurence Lars Svekis, Maaike van Putten, Rob Percival, Laurence Svekis, Codestars By Rob Percival(Authors)
  • 2021(Publication Date)
  • Packt Publishing

    (Publisher)

  5

  Loops

  We are starting to get a good basic grasp of JavaScript. This chapter will focus on a very important control flow concept: loops. Loops execute a code block a certain number of times. We can use loops to do many things, such as repeating operations a number of times and iterating over data sets, arrays, and objects. Whenever you feel the need to copy a little piece of code and place it right underneath where you copied it from, you should probably be using a loop instead.

  We will first discuss the basics of loops, then continue to discuss nesting loops, which is basically using loops inside loops. Also, we will explain looping over two complex constructs we have seen, arrays and objects. And finally, we will introduce two keywords related to loops, break and continue , to control the flow of the loop even more.

  There is one topic that is closely related to loops that is not in this chapter. This is the built-in foreach method. We can use this method to loop over arrays, when we can use an arrow function. Since we won't discuss these until the next chapter, foreach is not included here.

  These are the different loops we will be discussing in this chapter:

  • while loop
  • do while loop
  • for loop
  • for in
  • for of loop

  Note: exercise, project, and self-check quiz answers can be found in the Appendix .

  while loops

  The first loop we will discuss is the while loop . A while loop executes a certain block of code as long as an expression evaluates to true . The snippet below demonstrates the syntax of the while

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Java Programming

  • Joyce Farrell(Author)
  • 2018(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  C H A P T E R 6 Looping Upon completion of this chapter, you will be able to: Describe the loop structure Create while loops Use shortcut arithmetic operators Create for loops Create do…while loops Nest loops Improve loop performance Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 284 Looping C H A P T E R 6 Learning About the Loop Structure If making decisions is what makes programs seem smart, looping is what makes programs seem powerful. A loop is a structure that allows repeated execution of a block of statements. Within a looping structure, a Boolean expression is evaluated. If it is true, a block of statements called the loop body executes and the Boolean expression is evaluated again. The loop body can be a single statement, or a block of statements between curly braces. As long as the loop-controlling, Boolean expression is true, the statements in the loop body continue to execute. When the Boolean evaluation is false, the loop ends. One execution of any loop is called an iteration. Figure 6-1 shows a diagram of the logic of a loop. In Java, you can use several mechanisms to create loops. In this chapter, you learn to use three types of loops: • A while loop, in which the loop-controlling Boolean expression is the first statement in the loop, evaluated before the loop body ever executes • A for loop, which is usually used as a concise format in which to execute loops • A do…while loop, in which the loop- controlling Boolean expression is the last statement in the loop, evaluated after the loop body executes one time.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  An Object-Oriented Approach to Programming Logic and Design

  • Joyce Farrell(Author)
  • 2012(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  C H A P T E R 4 Looping In this chapter, you will learn about: The loop structure Using a loop control variable Nested loops Avoiding common loop mistakes Using a for loop Common loop applications Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Understanding the Loop Structure Although making decisions is what makes computers seem intelligent, looping makes computer programming both efficient and worthwhile. When you use a loop, you can write one set of instructions that operates on multiple data items. For example, a large company might use a single loop to produce thousands of paychecks, or a big-city utility company might use a single loop to process millions of customer bills. Using fewer instructions results in less time needed for design and coding, less compile time, and fewer errors. Recall the loop structure that you learned about in Chapter 2. Along with sequence and selection, it is one of the three basic structures used in structured programming. Figure 4-1 shows a loop structure. This loop starts with a test of a Boolean expression. The statements within a loop constitute the loop body ; the body executes as long as the loop-controlling Boolean expression remains true. The same loop-controlling question is asked following each execution of the loop body; the structure is exited only when the test expression is false. You may hear programmers refer to looping as repetition or iteration .

  Sign up to read

  Learn more about book