1 00:00:01,603 --> 00:00:04,610 Now let's come back to this problem 2 00:00:04,610 --> 00:00:06,700 of having some duplicated code 3 00:00:06,700 --> 00:00:08,132 and having all these extra cheques 4 00:00:08,132 --> 00:00:11,630 for whether something is a payment or a refund. 5 00:00:11,630 --> 00:00:13,360 We can solve this problem 6 00:00:13,360 --> 00:00:17,510 by utilizing factory functions and polymorphism. 7 00:00:17,510 --> 00:00:19,370 And for that of course, we need 8 00:00:19,370 --> 00:00:21,560 to understand what a factory function is 9 00:00:21,560 --> 00:00:23,391 and what polymorphism is. 10 00:00:23,391 --> 00:00:27,410 A factory function is simply a function which is used 11 00:00:27,410 --> 00:00:31,520 to produce something, for example, to produce objects 12 00:00:31,520 --> 00:00:35,170 or produce maps, arrays, anything like that. 13 00:00:35,170 --> 00:00:36,990 We provide a certain input, 14 00:00:36,990 --> 00:00:41,050 and it then produces a certain object for us. 15 00:00:41,050 --> 00:00:44,410 Polymorphism is a concept to which I will come back to 16 00:00:44,410 --> 00:00:46,530 in the next course section, 17 00:00:46,530 --> 00:00:49,040 which is about classes and objects. 18 00:00:49,040 --> 00:00:51,680 In the end, it means that we can have an object 19 00:00:51,680 --> 00:00:56,410 or a function, which we can always use in the same way, 20 00:00:56,410 --> 00:00:57,900 for example, an object 21 00:00:57,900 --> 00:01:01,100 on which we always can use the same method, 22 00:01:01,100 --> 00:01:04,060 but what this method does in detail, 23 00:01:04,060 --> 00:01:06,960 then depends on some other factors. 24 00:01:06,960 --> 00:01:10,670 And we can combine this to write a factory function, 25 00:01:10,670 --> 00:01:15,060 which produces different other functions or objects 26 00:01:15,060 --> 00:01:18,720 with functions that we can always call in the same way, 27 00:01:18,720 --> 00:01:22,190 but that then sometimes handle credit card payments, 28 00:01:22,190 --> 00:01:25,600 and sometimes handle PayPal refunds for example. 29 00:01:25,600 --> 00:01:28,770 And that is exactly what we're going to work on now. 30 00:01:28,770 --> 00:01:31,400 We're going to write a factory function, 31 00:01:31,400 --> 00:01:32,950 which creates an object, 32 00:01:32,950 --> 00:01:35,210 which always will have the same structure, 33 00:01:35,210 --> 00:01:36,650 but then different code 34 00:01:36,650 --> 00:01:39,503 that executes under different circumstances. 35 00:01:40,860 --> 00:01:44,660 Let's go up to the process transaction function again. 36 00:01:44,660 --> 00:01:49,660 Here I call process by method to then trigger this function. 37 00:01:51,010 --> 00:01:55,190 Now I will replace this function, so we'll add a new one, 38 00:01:55,190 --> 00:01:57,230 and soon delete the old one. 39 00:01:57,230 --> 00:02:01,973 And I will name this function get transaction processor. 40 00:02:03,710 --> 00:02:07,910 And this function will be a factory function. 41 00:02:07,910 --> 00:02:10,460 This function will return an object, 42 00:02:10,460 --> 00:02:13,660 and it will actually return a polymorphic object full 43 00:02:13,660 --> 00:02:16,530 of functions which always have the same name, 44 00:02:16,530 --> 00:02:18,550 but will do different things. 45 00:02:18,550 --> 00:02:19,710 That's the plan here. 46 00:02:19,710 --> 00:02:22,350 And for that, we will utilize the fact that 47 00:02:22,350 --> 00:02:24,830 in most programming languages, 48 00:02:24,830 --> 00:02:28,382 you can indeed use functions like regular values. 49 00:02:28,382 --> 00:02:33,090 So you can assign functions to variables to properties, 50 00:02:33,090 --> 00:02:35,040 you can pass functions around. 51 00:02:35,040 --> 00:02:37,100 And we're going to do that because we are going 52 00:02:37,100 --> 00:02:41,630 to return an object full of functions, which already exist, 53 00:02:41,630 --> 00:02:43,280 but which we won't call in here, 54 00:02:43,280 --> 00:02:46,210 but which we will just swap dynamically depending 55 00:02:46,210 --> 00:02:47,720 on which function we need. 56 00:02:47,720 --> 00:02:50,320 But it will become clearer as we start working 57 00:02:50,320 --> 00:02:52,140 on this factory function. 58 00:02:52,140 --> 00:02:55,460 And for this, I want to utilize the fact that functions 59 00:02:55,460 --> 00:02:57,110 in JavaScript but also 60 00:02:57,110 --> 00:03:01,320 in many other programming languages are callable, 61 00:03:01,320 --> 00:03:02,925 but don't have to be called. 62 00:03:02,925 --> 00:03:06,600 And if you don't add the brackets after the function name, 63 00:03:06,600 --> 00:03:09,300 you can use them just like any other value, 64 00:03:09,300 --> 00:03:12,690 like a string, a number or an object. 65 00:03:12,690 --> 00:03:15,376 So now with that, we can grab this code here, 66 00:03:15,376 --> 00:03:19,564 and move that into get transaction processor, 67 00:03:19,564 --> 00:03:22,963 and then add a new variable here, 68 00:03:23,880 --> 00:03:26,640 in this get transaction processor function, 69 00:03:26,640 --> 00:03:29,380 which in JavaScript, we do with the let keyword, 70 00:03:29,380 --> 00:03:31,677 which will name processors, 71 00:03:31,677 --> 00:03:33,997 because we have two possible processors 72 00:03:33,997 --> 00:03:38,730 for every transaction, a payment and a refund processor. 73 00:03:38,730 --> 00:03:41,630 At least after going through these cheques. 74 00:03:41,630 --> 00:03:44,109 Now in here in this object, which I create like this 75 00:03:44,109 --> 00:03:49,109 in JavaScript, or a map in other programming languages, 76 00:03:49,150 --> 00:03:51,053 I will add q keys. 77 00:03:52,360 --> 00:03:57,308 Payment with a value of null initially, so no value, 78 00:03:57,308 --> 00:04:00,863 and refund with a value of null initially. 79 00:04:02,990 --> 00:04:06,810 Now the idea is that we populate payment and refund 80 00:04:06,810 --> 00:04:11,780 with functions as values inside of these cheques. 81 00:04:11,780 --> 00:04:15,890 So here, if we use a credit card as a payment method, 82 00:04:15,890 --> 00:04:19,960 I will set processors.payment, 83 00:04:19,960 --> 00:04:23,400 equal to process credit card payment, 84 00:04:23,400 --> 00:04:25,460 but I'm not calling this function, 85 00:04:25,460 --> 00:04:28,743 I'm not adding parentheses, I'm just pointing at it. 86 00:04:29,590 --> 00:04:31,630 So this process credit card function 87 00:04:31,630 --> 00:04:34,610 which is defined down there, I'm pointing at it. 88 00:04:34,610 --> 00:04:37,750 I'm using it as a value, I'm not executing it. 89 00:04:37,750 --> 00:04:40,250 And I'm storing this pointer at this function 90 00:04:40,250 --> 00:04:43,033 in this key in this object or map. 91 00:04:44,740 --> 00:04:49,226 So here, I'll then do the same for refund and store process, 92 00:04:49,226 --> 00:04:53,670 credit card refund in the refund field of this map. 93 00:04:53,670 --> 00:04:55,318 Again just pointing at it. 94 00:04:55,318 --> 00:05:00,318 And we can now do this here, in all these cases, 95 00:05:00,360 --> 00:05:04,740 and just point at the different processor functions. 96 00:05:04,740 --> 00:05:07,010 So here it's process PayPal payment, 97 00:05:07,010 --> 00:05:11,809 at which I'm pointing here, it's process PayPal refund. 98 00:05:11,809 --> 00:05:15,530 And here it's process plan payment, 99 00:05:15,530 --> 00:05:18,363 and process plan refund. 100 00:05:19,390 --> 00:05:21,990 So now we're populating this object, 101 00:05:21,990 --> 00:05:26,220 and I am simply returning this object thereafter. 102 00:05:26,220 --> 00:05:29,041 So in this get transaction processor function, 103 00:05:29,041 --> 00:05:30,900 I'm creating this object, 104 00:05:30,900 --> 00:05:33,500 populating the different processors depending 105 00:05:33,500 --> 00:05:35,660 on the payment method, which was chosen, 106 00:05:35,660 --> 00:05:37,657 and then I return this. 107 00:05:37,657 --> 00:05:40,258 Now with that, we can get rid of the process 108 00:05:40,258 --> 00:05:44,430 by method, function, we should keep the is payment, 109 00:05:44,430 --> 00:05:46,262 and is refund helper functions, 110 00:05:46,262 --> 00:05:49,503 but we can get rid of the process credit card transaction, 111 00:05:49,503 --> 00:05:51,630 process PayPal transaction, 112 00:05:51,630 --> 00:05:54,026 and process plan transaction functions. 113 00:05:54,026 --> 00:05:57,330 So we remove a lot of code here. 114 00:05:57,330 --> 00:05:59,168 In get transaction processor, 115 00:05:59,168 --> 00:06:02,650 we should now accept the transaction as a parameter, 116 00:06:02,650 --> 00:06:05,164 because we're using it here to derive the method. 117 00:06:05,164 --> 00:06:07,341 And now we're creating this object here, 118 00:06:07,341 --> 00:06:08,885 which we can now utilize 119 00:06:08,885 --> 00:06:12,343 by calling get transaction processor, 120 00:06:14,570 --> 00:06:17,838 here in the process transaction function. 121 00:06:17,838 --> 00:06:20,530 Instead of calling process by method, 122 00:06:20,530 --> 00:06:22,660 we now get our processors, 123 00:06:22,660 --> 00:06:25,330 by calling get transaction processor, 124 00:06:25,330 --> 00:06:27,590 and passing the transaction to it. 125 00:06:27,590 --> 00:06:32,590 And now we can simply check if we have a payment 126 00:06:32,648 --> 00:06:34,849 for the given transaction, 127 00:06:34,849 --> 00:06:39,313 in which case, we want to call processors.payment, 128 00:06:39,313 --> 00:06:41,410 and execute this as a function, 129 00:06:41,410 --> 00:06:43,563 and pass the transaction to it, 130 00:06:44,560 --> 00:06:47,705 else we can call processors refund 131 00:06:47,705 --> 00:06:50,683 and pass the transaction as a function. 132 00:06:50,683 --> 00:06:53,313 And of course now we can also outsource this 133 00:06:53,313 --> 00:06:56,763 out of process transaction to keep it clean, 134 00:06:56,763 --> 00:06:59,086 and maybe add a new function here, 135 00:06:59,086 --> 00:07:04,086 which we call process with processor, 136 00:07:06,110 --> 00:07:10,089 accept the transactions argument and copy our code in there. 137 00:07:10,089 --> 00:07:12,544 And now it's processed with processor, 138 00:07:12,544 --> 00:07:13,998 which we can call here. 139 00:07:13,998 --> 00:07:15,171 Though again you can argue 140 00:07:15,171 --> 00:07:18,074 whether this really is a good split or not, 141 00:07:18,074 --> 00:07:20,609 it definitely makes this function more readable, 142 00:07:20,609 --> 00:07:23,000 but now of course we have to scroll down 143 00:07:23,000 --> 00:07:24,492 to process with processor. 144 00:07:24,492 --> 00:07:27,307 Still I would argue both functions are easy to find 145 00:07:27,307 --> 00:07:30,456 and readable and therefore clean. 146 00:07:30,456 --> 00:07:32,854 We could also rename these keys here, 147 00:07:32,854 --> 00:07:35,093 to make it clear that they hold functions, 148 00:07:35,093 --> 00:07:37,952 and rename this to make payment, 149 00:07:37,952 --> 00:07:42,952 and make refund for example, or process payment, 150 00:07:43,769 --> 00:07:46,049 and process refund, 151 00:07:46,049 --> 00:07:49,270 and of course then also use process payment here, 152 00:07:49,270 --> 00:07:50,848 when we store a function, 153 00:07:50,848 --> 00:07:55,552 and process refund when we store a function, 154 00:07:55,552 --> 00:07:57,835 and with these properties renamed, 155 00:07:57,835 --> 00:08:01,314 we can call process refund here, 156 00:08:01,314 --> 00:08:03,389 and process payment here. 157 00:08:03,389 --> 00:08:05,587 But that's just some renaming to make it clear 158 00:08:05,587 --> 00:08:07,787 of what's inside of these properties, 159 00:08:07,787 --> 00:08:11,558 which we of course should do to write clean code. 160 00:08:11,558 --> 00:08:12,989 And now with (indistinct) got rid 161 00:08:12,989 --> 00:08:15,443 of these extra nested if cheques. 162 00:08:15,443 --> 00:08:19,125 Because now we're using such a map of functions, 163 00:08:19,125 --> 00:08:20,412 which we return. 164 00:08:20,412 --> 00:08:24,563 So in the end get transaction processor is a function, 165 00:08:24,563 --> 00:08:27,716 which just returns a map of other functions, 166 00:08:27,716 --> 00:08:29,557 maybe therefore we should rename it 167 00:08:29,557 --> 00:08:32,730 to get transaction processors, 168 00:08:32,730 --> 00:08:37,289 and also call get transaction processors here of course. 169 00:08:37,289 --> 00:08:39,454 Because now this will give us an object 170 00:08:39,454 --> 00:08:41,479 or a map full of functions, 171 00:08:41,479 --> 00:08:43,260 which we then can call 172 00:08:43,260 --> 00:08:45,387 to process the transaction appropriately. 173 00:08:45,387 --> 00:08:50,103 And this is a technique we can use to make this code slimmer 174 00:08:50,103 --> 00:08:53,963 and to remove all these duplicate cheques.