Return a Value from a Function

You're learning that functions are a way to run several lines of JavaScript code by 0:00 issuing just a single command. 0:04 When you call a function, 0:06 you tell the JavaScript engine to jump to that function and run the code inside it. 0:07 Remember back when you said, go to the coffee shop, to your assistant? 0:11 They dashed off to the coffee shop. 0:15 When your assistant returned, they handed you coffee. 0:17 Well, functions can also give something back when they finish. 0:20 This is called, returning a value, and it's common when working with functions. 0:23 For example, let's say you needed a way to get the current time so 0:28 that you can display it on a web page. 0:32 You could create a function that gets the current time and 0:34 actually writes it to the page. 0:36 Better yet, you could create a function that just gets the time and 0:38 gives it back to you. 0:42 That way you can not only write the return value to the page, but 0:43 you could also use the return value in other ways, 0:46 like displaying it in an alert box, or printing it to the console. 0:49 In other words, creating a function that just does one thing, 0:53 returns the current time, makes the function flexible enough 0:56 that you can use it in many different situations. 0:59 To return a value from a function, you use the return keyword. 1:03 This creates what's called a return statement. 1:07 When the JavaScript engine, or 1:10 interpreter, encounters the return keyword, 1:12 it immediately jumps out of the current function and provides the value to return. 1:14 The value that's returned by the function can then be used in your program. 1:19 For example, in this case, the return value is given to the alert function. 1:23 So the message, your coffee is on its way, appears in an alert dialog box. 1:28 But you could use this return value in many different ways. 1:31 Print it to the console, or even save it in a variable. 1:34 Let's look at the alertRandom function we created earlier and 1:39 see how we can improve it. 1:41 Generating a random number from one to six is useful. 1:43 You can use to build a dice-rolling game, for example. 1:47 But the function we created is limited. 1:49 It generates a random number but always displays it in an alert box. 1:52 What if we wanted to show the random number on the page, 1:56 appear on the console, or store it in a variable? 1:58 We can make this function more useful by returning the random number only. 2:01 That way we could use it any way we wanted to. 2:05 I'll show you what I mean by first removing the alert method 2:07 from the function. 2:10 Next, I'll add a return statement to return a value from a function. 2:12 You use the return keyword. 2:16 And what do we want to return? 2:18 Well, the value stored in randomNumber. 2:20 So now the function name alertRandom doesn't make a whole lot of sense, 2:23 because the function no longer pops up an alert. 2:27 So I'll change it to getRandomNumber, because that's what it's now doing. 2:29 So now I can use this function anywhere I want to get a number from one to six. 2:37 For example, in an alert dialogue like this. 2:42 I can also print it to the console with the console.log method. 2:58 I can even store the function in a variable that I can use later. 3:11 For example, const dieRoll = a call to getRandomNumber. 3:15 And that's right, 3:22 a function call itself can be a value that gets stored in a variable. 3:23 Creating functions that only return a value is common in programming. 3:29 For example, you might create a function that computes the total cost of an item, 3:33 including tax and shipping. 3:37 The function would return that total cost so that you can use it in other ways, 3:38 like displayed on the web page, or use it for more calculations. 3:42 Lastly, functions always return a value, 3:47 even when they don't have a return statement. 3:49 If you don't specify a return value, the function returns undefined. 3:51 For example, in the console, 3:56 I’ll paste the alertRandom function we first wrote, then call it. 3:59 When I run this code, the browser pops up the alert, and 4:07 notice that undefined displays in the console. 4:10 Undefined is one of JavaScript's built-in values. 4:13 When returned by a function, it means that there's no return value specified. 4:16 Now, I'll call the getRandomNumber function here in the console. 4:22 And this time, the console inputs a random number value. 4:27