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JavaScript Quickstart

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Create Reusable Code with Functions

2:38 with Guil Hernandez

A function is a collection of code that performs a task or calculates a value.

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    So functions are at the heart of how JavaScript works. 0:00
    A function is a collection of code that does something as a function, right? 0:03
    So for example, prompt and alert 0:06
    are built in JavaScript functions you can use over and over again in your program. 0:09
    JavaScript also lets you define your own functions. 0:13
    To create a function, you type the keyword function 0:16
    followed by the name you want to give the function, for example, myFunction. 0:20
    Then a set of parentheses and a set of curly braces. 0:25
    In a function, the Java script you place inside 0:29
    the curly braces is run whenever the function is activated. 0:32
    Think of the code inside the braces as a set of instructions that you want to run 0:36
    each time the function is referenced in your code. 0:39
    So now I'm going to create a function that contains the same prompt and 0:42
    alert behavior we wrote earlier in the console. 0:46
    The function will ask for a user's name and say hello. 0:48
    So I'll name the function sayHello(). 0:51
    And between the curly braces, I'll add the response variable and the prompt and 0:57
    alert commands we wrote earlier. 1:02
    So I'll type var response and set it equal to prompt, 1:04
    passing it the message, what is your name? 1:11
    And below that I'll type alert and 1:19
    I'll pass alert("Hello", space followed by a plus sign then the response variable. 1:24
    Plus sign and an exclamation mark. 1:32
    So this functionality or 1:35
    set of instructions is now packaged up inside a function. 1:36
    I'll give this file a save, and nothing visually happens in the browser yet, 1:42
    even when I refresh. 1:47
    To activate the programming inside a function, you call the function. 1:48
    And to call a function and run the code inside it, you write 1:53
    the name of the function followed by a set of parentheses and a semicolon. 1:56
    So when you call a function, you're telling the JavaScript interpreter 2:03
    to jump to that function and run the code inside it. 2:07
    The syntax for calling a function should look familiar. 2:10
    Notice how alert and prompt are also calls to the alert and 2:13
    prompt functions built into JavaScript. 2:18
    Over in the browser I'll refresh, and now each time the sayHello function is called, 2:21
    we'll see the dialogue boxes pop up in the browser 2:26

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