1 00:00:01,250 --> 00:00:05,000 So now that you know how ES6 modules work, 2 00:00:05,000 --> 00:00:08,040 I just wanna quickly show you the module pattern 3 00:00:08,040 --> 00:00:09,890 that we used to use before 4 00:00:09,890 --> 00:00:13,400 in order to implement modules in JavaScript. 5 00:00:13,400 --> 00:00:15,630 And I believe that it's important 6 00:00:15,630 --> 00:00:18,240 that you understand this module pattern 7 00:00:18,240 --> 00:00:20,630 because you will still see it around, 8 00:00:20,630 --> 00:00:24,960 and it's also a very good application of many of the stuff 9 00:00:24,960 --> 00:00:27,410 that we have been learning throughout the course. 10 00:00:28,970 --> 00:00:29,970 Now, of course, 11 00:00:29,970 --> 00:00:33,750 just like in regular modules that we just learned about, 12 00:00:33,750 --> 00:00:36,370 the main goal of the module pattern 13 00:00:36,370 --> 00:00:38,860 is to encapsulate functionality, 14 00:00:38,860 --> 00:00:43,450 to have private data, and to expose a public API. 15 00:00:43,450 --> 00:00:46,150 And the best way of achieving all that 16 00:00:46,150 --> 00:00:48,530 is by simply using a function, 17 00:00:48,530 --> 00:00:52,060 because functions give us private data by default 18 00:00:52,060 --> 00:00:54,350 and allow us to return values, 19 00:00:54,350 --> 00:00:57,530 which can become our public API. 20 00:00:57,530 --> 00:01:01,580 So let's see how the module pattern is implemented. 21 00:01:01,580 --> 00:01:06,580 So we start by writing a function, okay? 22 00:01:06,980 --> 00:01:10,440 And usually we write an IIFE, actually. 23 00:01:10,440 --> 00:01:13,870 So an immediately invoked function expression. 24 00:01:13,870 --> 00:01:16,130 And the reason for that is because 25 00:01:16,130 --> 00:01:19,200 this way we don't have to call it separately 26 00:01:19,200 --> 00:01:24,200 and we can also ensure that it's only called once, right? 27 00:01:24,680 --> 00:01:29,313 And so for that, we wrap it like this and create an IIFE. 28 00:01:30,430 --> 00:01:32,550 So it's very important that this function 29 00:01:32,550 --> 00:01:36,200 is only created once because the goal of this function 30 00:01:36,200 --> 00:01:40,310 is not to reuse code by running it multiple times, 31 00:01:40,310 --> 00:01:42,290 the only purpose of this function 32 00:01:42,290 --> 00:01:46,053 is to create a new scope and return data just once. 33 00:01:47,020 --> 00:01:48,840 And then in here in the function, 34 00:01:48,840 --> 00:01:52,130 let's simply add the same variables 35 00:01:52,130 --> 00:01:56,293 that we had before in the other module. 36 00:01:57,570 --> 00:02:00,093 So let's do here again, a shopping cart. 37 00:02:01,810 --> 00:02:04,653 And so in that other shopping cart, 38 00:02:05,550 --> 00:02:08,720 we had a bunch of private variables, basically, 39 00:02:08,720 --> 00:02:11,440 so data that was not exported. 40 00:02:11,440 --> 00:02:14,750 And so we simply defined them as variables there, 41 00:02:14,750 --> 00:02:17,050 and here we do the same thing in the function. 42 00:02:18,580 --> 00:02:23,580 So total price 237, and total quantity 23. 43 00:02:30,460 --> 00:02:33,020 You can also use or add to cart, 44 00:02:33,020 --> 00:02:35,313 and let's simply grab that from here. 45 00:02:36,930 --> 00:02:38,783 So without the export, of course, 46 00:02:40,780 --> 00:02:42,420 and in this one, let's actually add 47 00:02:42,420 --> 00:02:45,140 another very simple function, 48 00:02:45,140 --> 00:02:47,573 which will simply lock something to the console, 49 00:02:48,930 --> 00:02:50,623 so this one is to order stock. 50 00:02:51,770 --> 00:02:55,230 So ordered from supplier, 51 00:02:55,230 --> 00:02:59,593 and let's call this one order stock. 52 00:03:00,940 --> 00:03:02,140 So right now, of course, 53 00:03:02,140 --> 00:03:04,200 all of this data here is private 54 00:03:04,200 --> 00:03:08,120 because it is inside of the scope of the function. 55 00:03:08,120 --> 00:03:12,150 And so now all we have to do is to return some of this stuff 56 00:03:12,150 --> 00:03:15,950 in order to basically return a public API. 57 00:03:15,950 --> 00:03:19,210 And so to do that, we simply return an object, 58 00:03:19,210 --> 00:03:23,780 which contains the stuff that we want to make public here. 59 00:03:23,780 --> 00:03:25,300 So let's say again, 60 00:03:25,300 --> 00:03:30,300 we want to add the add to cart function to the public API, 61 00:03:30,660 --> 00:03:35,567 also the cart array and total price and quantity. 62 00:03:38,880 --> 00:03:40,130 So basically in this case, 63 00:03:40,130 --> 00:03:45,130 everything except the order stock, okay? 64 00:03:45,460 --> 00:03:48,750 And of course we could have also defined all of these here, 65 00:03:48,750 --> 00:03:51,780 right in the object as properties and methods, 66 00:03:51,780 --> 00:03:53,520 but I find it a little bit cleaner 67 00:03:53,520 --> 00:03:55,700 to define everything outside 68 00:03:55,700 --> 00:03:57,770 and then to simply create an object, 69 00:03:57,770 --> 00:03:59,410 which contains everything 70 00:03:59,410 --> 00:04:02,650 that we want to expose to the outside. 71 00:04:02,650 --> 00:04:05,820 However, right now we are not really storing 72 00:04:05,820 --> 00:04:09,620 this returned object here anywhere, right? 73 00:04:09,620 --> 00:04:12,260 So if we run this right now, 74 00:04:12,260 --> 00:04:15,940 then this object kind of disappears into nothing. 75 00:04:15,940 --> 00:04:18,270 However, that's easy to fix 76 00:04:18,270 --> 00:04:20,890 because we can simply assign the result 77 00:04:20,890 --> 00:04:23,973 of running this IIFE here to a new variable. 78 00:04:25,030 --> 00:04:29,533 And so let's call this just like before, the shopping cart, 79 00:04:30,750 --> 00:04:32,763 let's say shopping cart two. 80 00:04:34,380 --> 00:04:36,950 And so now, just like before, 81 00:04:36,950 --> 00:04:41,950 we can now say shopping cart two.add to cart, 82 00:04:44,966 --> 00:04:49,966 and here let's say four apples and two pizzas, right? 83 00:04:54,820 --> 00:04:56,530 And so it works. 84 00:04:56,530 --> 00:04:59,093 And indeed, if we take a look at shopping cart, 85 00:05:00,800 --> 00:05:03,680 so shopping cart. 86 00:05:03,680 --> 00:05:05,860 Now, of course, now it's not available here 87 00:05:05,860 --> 00:05:09,040 because we are still inside of a module, 88 00:05:09,040 --> 00:05:11,300 and everything that is in a module 89 00:05:11,300 --> 00:05:13,680 is private to that very module. 90 00:05:13,680 --> 00:05:16,840 And so therefore we can now not access anything 91 00:05:16,840 --> 00:05:19,960 from this module here, here in the console, 92 00:05:19,960 --> 00:05:23,440 because this is your basically the global scope, 93 00:05:23,440 --> 00:05:27,060 but in the global scope, we are not creating any of this, 94 00:05:27,060 --> 00:05:30,760 so not even shopping carts too, right? 95 00:05:30,760 --> 00:05:35,347 So again, that's because it is scoped only to this module, 96 00:05:35,347 --> 00:05:39,500 but let's still take a look edit here in the console, 97 00:05:39,500 --> 00:05:41,960 so of course this we can do. 98 00:05:41,960 --> 00:05:43,570 And so here we see that indeed, 99 00:05:43,570 --> 00:05:47,840 we only exported these four things. 100 00:05:47,840 --> 00:05:51,460 Now, of course our cart now got manipulated, 101 00:05:51,460 --> 00:05:54,243 so that one that we defined here in the function, okay? 102 00:05:57,920 --> 00:06:00,160 But of course, on the other hand, 103 00:06:00,160 --> 00:06:05,000 the properties that we basically wanted to make private, 104 00:06:05,000 --> 00:06:06,740 they are not accessible. 105 00:06:06,740 --> 00:06:10,560 So we cannot do this, right? 106 00:06:10,560 --> 00:06:11,943 So they are undefined. 107 00:06:12,840 --> 00:06:15,440 All right, and that's actually it. 108 00:06:15,440 --> 00:06:18,820 That's the implementation of the module pattern. 109 00:06:18,820 --> 00:06:23,430 Now, do you understand exactly how and why this works? 110 00:06:23,430 --> 00:06:25,740 I mean, how do we, for example, 111 00:06:25,740 --> 00:06:28,490 have access to the cart variable here 112 00:06:28,490 --> 00:06:31,590 and even are able to manipulate it, 113 00:06:31,590 --> 00:06:34,150 so we see that it at changed, indeed. 114 00:06:34,150 --> 00:06:38,730 So how are we able to do that, even if this IIFE here, 115 00:06:38,730 --> 00:06:43,710 so this function has already returned long ago, right? 116 00:06:43,710 --> 00:06:45,150 So this function, of course, 117 00:06:45,150 --> 00:06:47,780 was only executed once in the beginning, 118 00:06:47,780 --> 00:06:51,150 and then all it did was to return this object 119 00:06:51,150 --> 00:06:54,950 and assigned it to this variable, right? 120 00:06:54,950 --> 00:06:57,440 But then we are able to use all of this 121 00:06:57,440 --> 00:06:59,380 and to also manipulate the data 122 00:06:59,380 --> 00:07:02,320 that is inside of this function, 123 00:07:02,320 --> 00:07:05,443 which is the function that returned this object. 124 00:07:06,480 --> 00:07:09,840 And the answer to how all of this works like this 125 00:07:09,840 --> 00:07:12,980 is one more time, closures. 126 00:07:12,980 --> 00:07:17,180 So closures, remember, allow a function to have access 127 00:07:17,180 --> 00:07:19,700 to all the variables that were present 128 00:07:19,700 --> 00:07:22,350 at its birthplace, basically. 129 00:07:22,350 --> 00:07:25,400 So that was a nice analogy that I used back then 130 00:07:25,400 --> 00:07:27,690 when we first talked about closures, 131 00:07:27,690 --> 00:07:30,660 and I think it's a very nice way to visualize 132 00:07:30,660 --> 00:07:33,090 how it works also in this case. 133 00:07:33,090 --> 00:07:38,090 So the add to cart function was created here, right? 134 00:07:38,150 --> 00:07:39,690 And so this function here 135 00:07:39,690 --> 00:07:42,650 is the birthplace of this function. 136 00:07:42,650 --> 00:07:46,040 And so therefore this function never loses connection 137 00:07:46,040 --> 00:07:49,643 to its birthplace, which was this function here. 138 00:07:50,640 --> 00:07:55,310 And so that birthplace, so to say, is all of this scope, 139 00:07:55,310 --> 00:07:58,140 which contains of course the cart. 140 00:07:58,140 --> 00:08:01,510 And so therefore the add to cart function out here 141 00:08:01,510 --> 00:08:04,240 can still access that cart variable 142 00:08:04,240 --> 00:08:07,440 that was in the function, okay? 143 00:08:07,440 --> 00:08:09,000 So the reason why this works 144 00:08:09,000 --> 00:08:13,560 is not because the cart variable is also in this object, 145 00:08:13,560 --> 00:08:15,000 so that's not relevant 146 00:08:15,000 --> 00:08:18,780 because here we are not using this.cart, right? 147 00:08:18,780 --> 00:08:20,203 We are simply using cart. 148 00:08:21,490 --> 00:08:22,920 So here we could also log 149 00:08:22,920 --> 00:08:27,120 something that is indeed private to this module. 150 00:08:27,120 --> 00:08:30,383 So something that will not be in this exported object. 151 00:08:31,270 --> 00:08:36,270 So let's say shipping cost is, and then shipping cost. 152 00:08:40,510 --> 00:08:43,640 And so in order to produce this string here, 153 00:08:43,640 --> 00:08:46,770 the function will also have to use this variable 154 00:08:46,770 --> 00:08:49,930 that was only present at its birthplace, 155 00:08:49,930 --> 00:08:53,853 but which no longer does exist besides that. 156 00:08:55,880 --> 00:08:58,190 So, indeed that still works, 157 00:08:58,190 --> 00:09:00,550 so the function is still able to access 158 00:09:00,550 --> 00:09:03,720 that value of 10, okay? 159 00:09:03,720 --> 00:09:06,940 And for an even deeper explanation of why this works, 160 00:09:06,940 --> 00:09:09,400 you can, of course, always go back and revisit 161 00:09:09,400 --> 00:09:11,750 that lecture about closures. 162 00:09:11,750 --> 00:09:14,470 Okay, but in essence, again, 163 00:09:14,470 --> 00:09:18,490 this is how the module pattern works and it works very well, 164 00:09:18,490 --> 00:09:22,340 and it has been working for a long time for developers, 165 00:09:22,340 --> 00:09:26,253 so long before ES6 modules even existed in JavaScript. 166 00:09:27,100 --> 00:09:31,250 Now, the problem is that if we wanted one module per file, 167 00:09:31,250 --> 00:09:33,550 like we have with ES6 modules, 168 00:09:33,550 --> 00:09:35,790 then we would have to create different scripts 169 00:09:35,790 --> 00:09:39,260 and link all of them in the HTML file. 170 00:09:39,260 --> 00:09:42,320 And that then creates a couple of problems, 171 00:09:42,320 --> 00:09:44,550 like we have to be careful with the order 172 00:09:44,550 --> 00:09:47,310 in which we declare them in HTML, 173 00:09:47,310 --> 00:09:49,300 and we would have all of the variables 174 00:09:49,300 --> 00:09:51,250 living in the global scope, 175 00:09:51,250 --> 00:09:54,710 and finally, we also couldn't bundle them together 176 00:09:54,710 --> 00:09:56,830 using a module bundler. 177 00:09:56,830 --> 00:09:59,610 And so as you learned at the beginning of this section, 178 00:09:59,610 --> 00:10:02,340 using a module bundler is very important 179 00:10:02,340 --> 00:10:04,420 in modern JavaScript. 180 00:10:04,420 --> 00:10:07,400 So the module pattern that we just learned about 181 00:10:07,400 --> 00:10:11,720 does indeed work quite good, but it has some limitations. 182 00:10:11,720 --> 00:10:13,330 And so that's exactly the reason 183 00:10:13,330 --> 00:10:17,593 why native modules were added to the language in ES6.