Functions

Quick reference

• 00:00 In this video I want to talk about functions, and
• 00:05 we are now well into our sort of intermediate JavaScript.
• 00:10 And functions, they're a little bit more complicated than what we've learned so
• 00:14 far, but they aren't too bad.
• 00:15 So, a function is basically a block of code
• 00:18 that is meant to perform a specific task.
• 00:21 So a function sits there until something else calls it, or we call it invoking it.
• 00:26 So some programming languages call these methods.
• 00:29 In Ruby, they call functions methods.
• 00:31 In JavaScript, they call them functions.
• 00:33 Functions, methods, they're basically the same thing.
• 00:35 So if you're familiar with methods in another programming language,
• 00:38 it's just a function in JavaScript.
• 00:39 So, let's go ahead and just build one here.
• 00:41 Jump right in and we start by calling the function key word.
• 00:45 And that's just function and then we give it some name.
• 00:49 Just call it someFunction for now and then, we put these parentheses
• 00:54 right next to it and we'll see what those are for in just a minute.
• 00:56 Then, do these curly braces again.
• 01:00 And everything between the curly braces, that's our stuff.
• 01:02 So, do something, right?
• 01:05 But everything inside here, that's the actual function.
• 01:08 That's the code that's going to be executed whenever we call this function,
• 01:11 whenever we invoke the function.
• 01:13 So, these parentheses are important, and
• 01:15 we can actually pass stuff into our function from the outside world.
• 01:19 So, if we said myNumber1 and then myNumber2.
• 01:26 Now, we can pass in things into this function and
• 01:29 do something with them inside.
• 01:31 So we can take, for instance, return myNumber 1 + myNumber 2,
• 01:38 and return I'm gonna say, functions return things.
• 01:44 You know, we're gonna run the code and
• 01:45 we're gonna return the output back to the real world.
• 01:48 So myNumber1 and myNumber2, those are called parameters, and
• 01:52 like I said we can pass things in.
• 01:54 So lets play around with this.
• 01:55 To invoke a function or call a function, we just type in the name of the function,
• 02:00 someFunction, and then parentheses.
• 02:03 And that'll do it.
• 02:04 That invokes the function.
• 02:05 Now if we wanna actually pass parameters into the function, we do it right here.
• 02:10 So I might go 1 and 4.
• 02:12 Now this is gonna pass 1 into myNumber1, and it's gonna pass 4 into myNumber2.
• 02:18 So if we run this, actually let's go document.write
• 02:27 Pass this in.
• 02:28 So we're passing in 1 and 4, and we're adding 1 and 4 so we should get 5.
• 02:33 We got absolutely nothing though, I misspelled function.
• 02:36 My spelling is terrible.
• 02:38 Boom. There we go, five.
• 02:40 So we can flat out call a function,
• 02:42 we can invoke a function like we just did right here, just by calling it.
• 02:45 Or, we can assign the output of a function to a variable, and
• 02:48 then do something with the variable.
• 02:50 So, we can go var myVariable equals someFunction and
• 02:57 then let's pass it 1 and 5.
• 03:02 And then, down here we can just output myVariable.
• 03:08 See what we're doing here?
• 03:09 We're saying assign the output of some function into this variable, and
• 03:13 then just print mVariable to the screen.
• 03:15 So if we save this, we should should get six.
• 03:17 Okay. Reload. Because one and five is six.
• 03:19 So that's pretty cool.
• 03:20 So, why should we use functions?
• 03:22 Well, they allow us to create little programs and
• 03:24 then reuse them whenever we want to.
• 03:26 So, once it's written, you can call a function whenever you want, over and
• 03:30 over again, as often as you want whenever.
• 03:32 You just invoke it with its name in the parentheses like we just did.
• 03:36 So those are functions.
• 03:37 They're really one of the fundamental building blocks of any programming
• 03:40 language, but I think you'll agree that they're not that complicated.
• 03:43 And that's all for this video.
• 03:44 In the next video, I want to talk about if-then statements.

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