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[MUSIC]

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Hi, everyone, I'm Guil, a developer and
instructor here at Treehouse.

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In this course,
I'll teach you another fundamental concept

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that you'll use just about every day
in JavaScript programming, loops.

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[MUSIC]

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In programming, a loop is a way to repeat
the same set of actions a certain number

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of times or
until a specific condition is true.

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For example, let's say you wanted to
display ten random numbers on a web page.

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Well, you could write the code
to generate a random number,

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then display it on the page.

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Then write that exact code a second time,
a third time,

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a fourth time, until you've
duplicated that same code ten times.

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Well, typing the same code ten times seems
like a lot of work, not only for you, but

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also for other developers who
might work with your code.

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Now, imagine you wanted
100 random numbers or

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a 1,000,
that would be a lot of repetitive code.

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Here's a better way, automate it, write
that code once, then have your program

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repeat it 10 times, or a 100, or a 1,000
times, that's exactly what a loop does.

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Think of a loop as a running track
with entrance and exit areas.

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Imagine you're putting
together a 10,000 meter race,

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you could build one really long path for
the runners to run on.

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But that would take up a lot of space,
it would take a long time to build and

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would be very expensive.

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Or you could create a much shorter path
that racers can run around over and

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over again.

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The oval shape of the track is a loop and

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a race requires the runners to run around
that track a certain number of times.

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When a runner has gone around
the track ten times, for example,

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then that runner has completed the race.

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Programming loops also look like this,

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the code you want to run more
than once is inside the loop.

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When you enter the loop, the code inside
it runs once, then it runs again and

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again until a particular condition is met.

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For example, when the loop has
run ten times, the loop ends.

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Loops are really common in programming and

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there are different ways to
write loops in JavaScript.

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Some use different mechanisms and

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syntax making certain loops a better
choice over others in specific situations.

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You'll learn three types of loops in this
course, the while, do-while, and for loop.

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Before we keep going, you should know
that I'm going to assume that you

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already know the basics of
JavaScript variables, strings,

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numbers, conditionals, and functions.

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So to help you succeed, you should
have completed the prerequisites for

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this course.

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You can review them in
the teacher's notes with this video.