1 00:00:00,420 --> 00:00:04,050 So this video is going to be the last one on functions for a little bit. 2 00:00:04,050 --> 00:00:07,530 And we're going to talk about a concept called the higher order functions. 3 00:00:07,530 --> 00:00:13,950 So higher order functions are functions that either take a function as an argument or they return another 4 00:00:13,950 --> 00:00:14,970 function. 5 00:00:15,510 --> 00:00:20,850 So yes this is possible and not only is it possible it's something that we'll be doing a lot especially 6 00:00:20,850 --> 00:00:22,190 later in this course. 7 00:00:22,380 --> 00:00:27,900 So I'm going to show you an initial example something called set interval and what set interval does 8 00:00:28,230 --> 00:00:34,140 is it takes a function and it will call that function at a specific interval that we provide. 9 00:00:34,140 --> 00:00:38,340 So it's a way to have something repeat every second or every half a second. 10 00:00:38,400 --> 00:00:42,340 Right now with a loop we can repeat things but it happens immediately. 11 00:00:42,360 --> 00:00:45,010 So set interval we can time it out. 12 00:00:45,840 --> 00:00:48,790 So let's go ahead and take a look at how set interval works. 13 00:00:49,170 --> 00:00:54,300 And before we actually dive into that we need to define a function that we are going to pass to set 14 00:00:54,330 --> 00:00:55,210 interval. 15 00:00:55,260 --> 00:00:58,750 So we're going to write code to sing Twinkle twinkle little star again. 16 00:00:58,800 --> 00:01:04,410 We're just going to abreviated and we're going to schedule it to run using set interval every second 17 00:01:04,430 --> 00:01:04,700 . 18 00:01:04,950 --> 00:01:07,620 So first we need to write the twinkle twinkle code. 19 00:01:07,710 --> 00:01:15,270 So I'm going to do a function sing and that's just going to come to don't log. 20 00:01:15,270 --> 00:01:17,370 Twinkle twinkle. 21 00:01:17,970 --> 00:01:19,340 And then another line 22 00:01:22,170 --> 00:01:28,100 I wonder and we'll just leave it at that so I can call sing myself. 23 00:01:28,200 --> 00:01:29,580 Just like that. 24 00:01:29,730 --> 00:01:31,600 And that works great. 25 00:01:31,650 --> 00:01:39,060 So next what we want to do is use set interval to make sing or to call sing every 1000 milliseconds 26 00:01:39,060 --> 00:01:40,100 or every second. 27 00:01:40,410 --> 00:01:45,490 So to do that I'm going to define the pattern here so set interval takes two arguments. 28 00:01:45,540 --> 00:01:49,340 It's just a function but it takes another function as its argument. 29 00:01:49,380 --> 00:01:53,230 The first one is just we'll call it another funk. 30 00:01:53,430 --> 00:01:57,060 And the second one is the interval in milliseconds. 31 00:01:57,060 --> 00:01:58,560 So I'm going to fill this out now. 32 00:01:58,720 --> 00:02:08,730 Another phone call the function we want it to call is called Sing and the interval is 1000 milliseconds 33 00:02:08,730 --> 00:02:09,180 . 34 00:02:09,390 --> 00:02:14,750 Or we could do every half a second 500 milliseconds or one millisecond which would be insanely fast 35 00:02:14,890 --> 00:02:17,110 but we're going to do 1000 milliseconds. 36 00:02:17,130 --> 00:02:23,920 So this is going to call whatever's inside of sing these two lines every 1000 milliseconds. 37 00:02:23,970 --> 00:02:29,700 And when I hit Enter you'll see that it starts to happen. 38 00:02:29,700 --> 00:02:35,040 The other thing I just want to call your attention to before it disappears is that when Iran set interval 39 00:02:35,460 --> 00:02:37,320 it returns this number two. 40 00:02:37,470 --> 00:02:39,840 So we'll see what that's used for and just a moment. 41 00:02:40,410 --> 00:02:45,720 So another thing that you might be asking is why do we not need parentheses after seeing. 42 00:02:46,050 --> 00:02:52,440 And the reason for that is that we're not the one calling saying set interval is actually calling saying 43 00:02:53,100 --> 00:02:54,590 every 1000 seconds. 44 00:02:54,900 --> 00:02:56,430 So we don't want to execute it. 45 00:02:56,460 --> 00:02:58,570 We want to let's set interval executed. 46 00:02:58,740 --> 00:03:05,130 So what we do is just pass the value of saying we're just passing the name Singh and the code inside 47 00:03:05,130 --> 00:03:05,750 of it. 48 00:03:05,940 --> 00:03:07,220 But we're not running it. 49 00:03:07,260 --> 00:03:09,470 We leave that to set interval. 50 00:03:09,690 --> 00:03:16,200 So to stop set interval we need to use this number to set interval returns a number and we can use that 51 00:03:16,200 --> 00:03:18,300 number to stop it. 52 00:03:18,300 --> 00:03:24,720 So there's another function clear interval and we just give it that number two or it might be another 53 00:03:24,720 --> 00:03:26,160 number in your case. 54 00:03:26,160 --> 00:03:33,420 So to sum this up set interval is just one example of a higher order function and a higher order function 55 00:03:33,780 --> 00:03:37,480 is one where we can pass another function to it as an argument. 56 00:03:37,860 --> 00:03:43,040 And we could return another function which we haven't seen yet but most often we'll be passing a function 57 00:03:43,380 --> 00:03:45,210 to another function. 58 00:03:45,210 --> 00:03:52,560 So there's one other change we could make which is sometimes we want to run some code every second. 59 00:03:52,560 --> 00:03:54,310 For instance set interval. 60 00:03:54,420 --> 00:03:58,390 But we don't want to define a separate function ahead of time. 61 00:03:59,430 --> 00:04:07,470 So instead of saying here I don't have a function yet and I want to write it right here I could do that 62 00:04:07,770 --> 00:04:10,170 with something called an anonymous function. 63 00:04:10,350 --> 00:04:13,240 And that looks like this. 64 00:04:13,290 --> 00:04:17,850 So I write function but I don't give it a name because I'm never going to use it again. 65 00:04:17,970 --> 00:04:20,190 I'm just giving it to set interval. 66 00:04:20,250 --> 00:04:27,590 So function parentheses and then inside of here I'll write my code and I'm going to hit enter. 67 00:04:27,720 --> 00:04:32,050 So inside of these braces I put my canceled out log. 68 00:04:32,910 --> 00:04:41,580 I am anonymous function and control that log. 69 00:04:41,580 --> 00:04:43,240 This is awesome. 70 00:04:44,100 --> 00:04:45,270 All right. 71 00:04:45,270 --> 00:04:52,210 So then I need to add my interval comma and let's do this every two seconds. 72 00:04:52,290 --> 00:04:54,790 So this is a little bit hectic looking. 73 00:04:54,960 --> 00:05:04,350 Coming from our simple swing set interval what we're doing though is defining the function right here 74 00:05:04,380 --> 00:05:05,200 in line. 75 00:05:05,400 --> 00:05:08,580 So this is not something we can call outside of set interval. 76 00:05:08,580 --> 00:05:13,220 It's purely a way to pass a group of code into set interval. 77 00:05:13,410 --> 00:05:15,230 And then the second argument is the same. 78 00:05:15,240 --> 00:05:16,530 It's just another number. 79 00:05:16,800 --> 00:05:19,850 And if I do this you'll see every two seconds. 80 00:05:20,010 --> 00:05:21,580 It calls this code. 81 00:05:22,250 --> 00:05:24,470 But I have no way to call this function again. 82 00:05:24,660 --> 00:05:26,010 Outside of it. 83 00:05:26,190 --> 00:05:31,740 So we will see anonymous functions quite a bit more later in this class and almost always we use them 84 00:05:31,860 --> 00:05:35,130 when we're passing in a function to another function. 85 00:05:35,130 --> 00:05:39,870 So if this is still a little hazy for you don't worry we're going to spend a lot more time using these 86 00:05:40,320 --> 00:05:41,530 things like set interval. 87 00:05:41,550 --> 00:05:45,100 But also some other functions that we're going to introduce in a few videos from now.