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Another feature of VS2015
is default parameters.

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Default parameters let you
set default values for

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parameters accepted by a function.

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If you're familiar with other
programming languages you're probably

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already familiar with the concept.

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You can call a function and
if you don't pass a value for

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certain parameters the function can fill
in those blanks with the default values.

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You can follow along using
the latest workspace by

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launching the workspace on this page.

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Suppose we have a function.

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We'll call it greet.

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It takes two parameters, name and time of
day, and it logs a message to the console.

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Now in ES5, we could check the arguments
passed into the function and

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set default values.

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So for example we can say
name = name | | 'guil' and

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time of day = time of day double pipe day.

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So here the double pipe
checks the variable.

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And returns the value of the variable.

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If it's true, the otherwise it returns
the default value on the right side.

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If I call this greet function and
run the file in the console.

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I see the message Good Day, Guil!

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In ES 2015 we can set default values for

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the parameters we pass to a function
simply by adding an equal sign in a value.

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So I'll delete the name and time of day
variables a nd values I just wrote.

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And right up here,
the values we pass can be a string,

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Boolean, object, array or a function.

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So, in this case, let's give our
parameters strings for default values.

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So we'll say name = Guil and
time of day = day.

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So, now even when I don't
provide a name or time of day.

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The council will still log.

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Good Day, Guil to the console.

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So, now let's try something different.

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I'm okay with the default value for
a name but

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I wanna provide my greeting
a different value for time of day.

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To do this, I need to pass the function
undefined as the value for

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the name parameter.

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You see, parameters with a default
value are considered optional.

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So we pass undefined to tell
the interpreter to use the default value.

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And then I'll set the second
parameter to afternoon.

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So now when I run the file in the console,
it logs the message, good afternoon Guil.

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Why thank you, console.

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Default parameters are easy
to start using, and

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will help your code be readable and
maintainable in the future.

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In the next video I'll teach you about
rest parameters and spread operators.