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JavaScript has a particular operator to test more than one condition. It's called a logical "AND" operator, represented by two ampersands (&&).
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Sometimes, a single condition
isn't enough to make a decision.
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For example,
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even if it's a hot day, you don't wanna go
swimming if you don't know how to swim.
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In this case, you might ask,
if it's a hot day and I know how to swim,
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then I'll go swimming.
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There are two tests here.
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Is it a hot day and do I know how to swim?
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In order to move on to the action going
swimming, they both have to be true.
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If the first condition is false,
for example, it's not a hot day,
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then no action is taken.
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If the second condition is false,
I don't know
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how to swim It doesn't matter if it's
a hot day, I won't be going swimming.
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JavaScript has a special operator
to test more than one condition.
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It's called an AND operator and
is represented by two ampersands.
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You place one condition on either
side of the two ampersands.
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The two conditions
are evaluated separately, but
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work together to create a single
Boolean value, true or false.
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For example,
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let's say you want to test if a variable
holds a number between 20 and 30.
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Well, there's no single comparison
operator you can use to check if a number
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lies within a specific range.
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However, you can use the logical AND
operator for this,
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I'll demonstrate using
the JavaScript console.
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You can follow along too, if you'd like.
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In the console, I'll declare
a variable named age and set it to 25.
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I can test the value in
this variable like this.
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What we really have here
are two separate conditions.
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20 is less than age and
age is less than 30.
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Each condition is tested separately and
produces its own true or false value.
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We know that the value in
the age variable is 25.
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So the first test asks,
if 20 is less than age.
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In other words, is 20 less than 25?
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Yes, it is.
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So this first condition is true.
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The second test asks, if age is
less than 30, is 25 less than 30?
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Yes, it is.
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So this condition is also true.
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The role of the logical AND
operator is to combine the two tests.
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It asks, is condition one true and
is condition two true?
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In this case, yes, they are both true.
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So I wanna run this by pressing Enter.
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You can see that the result
is a true value.
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Let's continue with a few more examples.
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I'll change the value of
the age variable to 35,
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then press the up arrow key twice
to bring back the conditions.
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Now the first condition is true,
because 20 is less than 35.
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But the second condition,
35 is less than 30 is false.
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So notice how the entire
condition evaluates to false.
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All right,
how about I set the value of age to 10?
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Now the first condition is false and
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the second condition is true,
because 10 is less than 30.
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But it doesn't matter since
just one of these is false,
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the entire condition evaluates to false.
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Finally, let's say there's
a string value in the variable.
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Well, that isn't a number at all.
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So it can't be compared to a number.
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In this case, both tests are false.
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And logically enough,
the entire condition evaluates to false.
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As you can see, the AND
operator is pretty strict.
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Use the and
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operator whenever you need two conditions
to pass before starting an action.
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For example,
say you have a login form on your website.
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You might check to see
that both the username and
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password fields are filled out
before submitting the form.
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If both the username and password fields
are empty, then don't submit the form.
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