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So functions are at the heart
of how JavaScript works.

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A function is a collection of code that
does something as a function, right?

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So for example, prompt and alert

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are built in JavaScript functions you can
use over and over again in your program.

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JavaScript also lets you
define your own functions.

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To create a function,
you type the keyword function

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followed by the name you want to give
the function, for example, myFunction.

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Then a set of parentheses and
a set of curly braces.

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In a function,
the Java script you place inside

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the curly braces is run whenever
the function is activated.

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Think of the code inside the braces as
a set of instructions that you want to run

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each time the function is
referenced in your code.

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So now I'm going to create a function
that contains the same prompt and

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alert behavior we wrote
earlier in the console.

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The function will ask for
a user's name and say hello.

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So I'll name the function sayHello().

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And between the curly braces, I'll add
the response variable and the prompt and

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alert commands we wrote earlier.

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So I'll type var response and
set it equal to prompt,

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passing it the message, what is your name?

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And below that I'll type alert and

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I'll pass alert("Hello", space followed by
a plus sign then the response variable.

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Plus sign and an exclamation mark.

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So this functionality or

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set of instructions is now
packaged up inside a function.

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I'll give this file a save, and nothing
visually happens in the browser yet,

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even when I refresh.

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To activate the programming inside
a function, you call the function.

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And to call a function and
run the code inside it, you write

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the name of the function followed by
a set of parentheses and a semicolon.

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So when you call a function,
you're telling the JavaScript interpreter

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to jump to that function and
run the code inside it.

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The syntax for
calling a function should look familiar.

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Notice how alert and
prompt are also calls to the alert and

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prompt functions built into JavaScript.

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Over in the browser I'll refresh, and now
each time the sayHello function is called,

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we'll see the dialogue
boxes pop up in the browser