1 00:00:02,050 --> 00:00:05,260 When you have deeply nested code like this, 2 00:00:05,260 --> 00:00:08,480 it can be overwhelming if you look at this code. 3 00:00:08,480 --> 00:00:10,340 Where should you start? 4 00:00:10,340 --> 00:00:12,470 Well, you're going to see various ways 5 00:00:12,470 --> 00:00:15,090 of slimming this down and making it cleaner 6 00:00:15,090 --> 00:00:16,530 throughout this module 7 00:00:16,530 --> 00:00:18,510 but one very efficient tweak, 8 00:00:18,510 --> 00:00:20,712 which you can make in a lot of cases 9 00:00:20,712 --> 00:00:23,540 is that you use so-called guards 10 00:00:23,540 --> 00:00:26,000 and that you fail fast. 11 00:00:26,000 --> 00:00:27,770 Now, what does this mean? 12 00:00:27,770 --> 00:00:30,230 Take a look at this simple snippet. 13 00:00:30,230 --> 00:00:31,980 We have a if check here 14 00:00:31,980 --> 00:00:34,860 where we check whether an email includes a @ sign 15 00:00:34,860 --> 00:00:36,080 and if that's the case, 16 00:00:36,080 --> 00:00:39,500 we do a bunch of work inside of that if statement. 17 00:00:39,500 --> 00:00:42,840 And that bunch of work could be multiple lines of code. 18 00:00:42,840 --> 00:00:45,850 It could be as much as all the code you have here 19 00:00:45,850 --> 00:00:47,510 in the outermost if statement. 20 00:00:47,510 --> 00:00:49,960 So all this code here ultimately 21 00:00:49,960 --> 00:00:52,363 is in this one if check here. 22 00:00:53,460 --> 00:00:55,370 Now, if you have a case like this, 23 00:00:55,370 --> 00:00:58,290 you often can use a guard, 24 00:00:58,290 --> 00:01:01,660 which means you simply invert the if check, 25 00:01:01,660 --> 00:01:04,440 for example, in this case, by checking for the opposite 26 00:01:04,440 --> 00:01:05,890 with an exclamation mark. 27 00:01:05,890 --> 00:01:09,490 So for the email not including the @ sign, 28 00:01:09,490 --> 00:01:11,000 and this is JavaScript 29 00:01:11,000 --> 00:01:14,050 but of course, you can do this in any programming language. 30 00:01:14,050 --> 00:01:16,670 The exact syntax might just matter. 31 00:01:16,670 --> 00:01:19,240 And then you do one important other thing. 32 00:01:19,240 --> 00:01:22,680 You just return inside of that if statement. 33 00:01:22,680 --> 00:01:25,350 And that means that you now use this if check 34 00:01:25,350 --> 00:01:26,490 as a guard. 35 00:01:26,490 --> 00:01:30,070 It runs before your main code runs 36 00:01:30,070 --> 00:01:32,610 and if you make it into this if check, 37 00:01:32,610 --> 00:01:34,710 so if some condition is not met, 38 00:01:34,710 --> 00:01:37,770 in this case, if the email does not include a @ sign, 39 00:01:37,770 --> 00:01:39,799 then you fail fast, 40 00:01:39,799 --> 00:01:42,520 which means you return, 41 00:01:42,520 --> 00:01:45,000 which in the context of a function means 42 00:01:45,000 --> 00:01:46,133 that the code thereafter, 43 00:01:46,133 --> 00:01:50,068 all the code after the if statement won't execute. 44 00:01:50,068 --> 00:01:53,250 This is what makes this if statement a guard. 45 00:01:53,250 --> 00:01:55,550 It guards the rest of the code. 46 00:01:55,550 --> 00:01:57,460 If this condition is not met 47 00:01:57,460 --> 00:02:01,140 because we fail fast, we avoid that the other code 48 00:02:01,140 --> 00:02:02,600 will run at all. 49 00:02:02,600 --> 00:02:05,830 And we had the same behavior on the left side 50 00:02:05,830 --> 00:02:09,090 but there, the to be executed code was inside 51 00:02:09,090 --> 00:02:10,170 of the if statement 52 00:02:10,170 --> 00:02:12,960 and therefore, it was nested inside of it, 53 00:02:12,960 --> 00:02:14,980 making it harder to read. 54 00:02:14,980 --> 00:02:17,600 A guard is typically way easier to read 55 00:02:17,600 --> 00:02:18,839 and to understand. 56 00:02:18,839 --> 00:02:22,460 And you cannot just use that if you have one if statement, 57 00:02:22,460 --> 00:02:24,400 which wraps all your other code. 58 00:02:24,400 --> 00:02:25,800 You can also use a guard 59 00:02:25,800 --> 00:02:27,680 if you have a nested if statement 60 00:02:27,680 --> 00:02:29,690 in another if statement. 61 00:02:29,690 --> 00:02:31,180 For example, let's say here. 62 00:02:31,180 --> 00:02:32,800 hasPurchases. 63 00:02:32,800 --> 00:02:34,430 We could also outsource this 64 00:02:34,430 --> 00:02:37,730 and turn this into a guard where we fail fast 65 00:02:37,730 --> 00:02:40,650 so that we then have two consecutive if statements 66 00:02:40,650 --> 00:02:43,570 instead of one deeply nested one. 67 00:02:43,570 --> 00:02:45,690 And this is a super efficient technique 68 00:02:45,690 --> 00:02:49,270 for removing unnecessary nesting. 69 00:02:49,270 --> 00:02:51,323 Now, let's apply it to our example.