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JavaScript Loops

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What is a Loop?

2:36 with Guil Hernandez

In programming, a loop is a way to repeat the same set of actions a certain number of times or until a specific condition is true.

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    [MUSIC] 0:00
    Hi, everyone, I'm Guil, a developer and instructor here at Treehouse. 0:09
    In this course, I'll teach you another fundamental concept 0:13
    that you'll use just about every day in JavaScript programming, loops. 0:16
    [MUSIC] 0:20
    In programming, a loop is a way to repeat the same set of actions a certain number 0:24
    of times or until a specific condition is true. 0:28
    For example, let's say you wanted to display ten random numbers on a web page. 0:32
    Well, you could write the code to generate a random number, 0:37
    then display it on the page. 0:40
    Then write that exact code a second time, a third time, 0:42
    a fourth time, until you've duplicated that same code ten times. 0:45
    Well, typing the same code ten times seems like a lot of work, not only for you, but 0:49
    also for other developers who might work with your code. 0:53
    Now, imagine you wanted 100 random numbers or 0:57
    a 1,000, that would be a lot of repetitive code. 0:59
    Here's a better way, automate it, write that code once, then have your program 1:03
    repeat it 10 times, or a 100, or a 1,000 times, that's exactly what a loop does. 1:07
    Think of a loop as a running track with entrance and exit areas. 1:13
    Imagine you're putting together a 10,000 meter race, 1:16
    you could build one really long path for the runners to run on. 1:20
    But that would take up a lot of space, it would take a long time to build and 1:23
    would be very expensive. 1:27
    Or you could create a much shorter path that racers can run around over and 1:29
    over again. 1:34
    The oval shape of the track is a loop and 1:35
    a race requires the runners to run around that track a certain number of times. 1:37
    When a runner has gone around the track ten times, for example, 1:42
    then that runner has completed the race. 1:45
    Programming loops also look like this, 1:47
    the code you want to run more than once is inside the loop. 1:49
    When you enter the loop, the code inside it runs once, then it runs again and 1:53
    again until a particular condition is met. 1:57
    For example, when the loop has run ten times, the loop ends. 2:00
    Loops are really common in programming and 2:04
    there are different ways to write loops in JavaScript. 2:06
    Some use different mechanisms and 2:09
    syntax making certain loops a better choice over others in specific situations. 2:10
    You'll learn three types of loops in this course, the while, do-while, and for loop. 2:16
    Before we keep going, you should know that I'm going to assume that you 2:21
    already know the basics of JavaScript variables, strings, 2:24
    numbers, conditionals, and functions. 2:27
    So to help you succeed, you should have completed the prerequisites for 2:29
    this course. 2:32
    You can review them in the teacher's notes with this video. 2:33

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