1 00:00:01,080 --> 00:00:03,980 Do you remember how we chained array methods 2 00:00:03,980 --> 00:00:08,980 one after another, for example filter map and reduce? 3 00:00:09,230 --> 00:00:11,440 So by chaining these methods, 4 00:00:11,440 --> 00:00:13,720 we could first filter an array, 5 00:00:13,720 --> 00:00:15,400 then map the result. 6 00:00:15,400 --> 00:00:18,400 And finally reduce the results of the map, 7 00:00:18,400 --> 00:00:20,860 all in one line of code. 8 00:00:20,860 --> 00:00:23,910 And we can actually implement the same ability 9 00:00:23,910 --> 00:00:28,080 of chaining methods in the methods of our class. 10 00:00:28,080 --> 00:00:30,163 And so let's go do that now. 11 00:00:31,620 --> 00:00:35,320 And actually, this is extremely easy to do. 12 00:00:35,320 --> 00:00:39,170 So all we have to do is to return the object itself 13 00:00:39,170 --> 00:00:42,043 at the end of a method that we want to be chainable. 14 00:00:42,920 --> 00:00:46,363 So let's say that we wanted to do this. 15 00:00:47,730 --> 00:00:50,143 So let me take that away from here. 16 00:00:52,130 --> 00:00:53,223 So chaining. 17 00:00:55,210 --> 00:00:58,423 So let's say we wanted to do account, 18 00:00:59,650 --> 00:01:01,520 and then deposit, 19 00:01:01,520 --> 00:01:03,780 let's say, 300. 20 00:01:03,780 --> 00:01:06,200 And then right afterwards, we wanted 21 00:01:06,200 --> 00:01:08,513 to deposit again on the same account. 22 00:01:09,390 --> 00:01:13,570 So we would like to call deposit again, right away, 23 00:01:13,570 --> 00:01:16,000 let's say 500 this time. 24 00:01:16,000 --> 00:01:18,660 And then immediately after that, 25 00:01:18,660 --> 00:01:21,203 let's say we want to withdraw 35. 26 00:01:22,610 --> 00:01:26,830 Maybe we also want to request a loan in the middle of this. 27 00:01:26,830 --> 00:01:30,973 So request loan, let's say 25,000. 28 00:01:31,810 --> 00:01:34,983 And then finally, we want to withdraw some more, 29 00:01:36,010 --> 00:01:37,223 let's say 4000. 30 00:01:38,200 --> 00:01:40,593 So right now, this is not gonna work. 31 00:01:41,570 --> 00:01:43,480 So let's see the error. 32 00:01:43,480 --> 00:01:46,830 And so the problem here is that... 33 00:01:46,830 --> 00:01:49,020 this one here will work. 34 00:01:49,020 --> 00:01:51,870 But this will then return nothing. 35 00:01:51,870 --> 00:01:53,453 Because let's see, 36 00:01:54,450 --> 00:01:57,830 the deposit method does return undefined 37 00:01:57,830 --> 00:02:01,133 because we're not returning anything explicitly here. 38 00:02:02,730 --> 00:02:05,610 And so then undefined gets returned. 39 00:02:05,610 --> 00:02:07,740 And so then here, in this next one 40 00:02:07,740 --> 00:02:11,860 we are trying to call the deposit method on undefined 41 00:02:11,860 --> 00:02:14,110 which is the result of all this. 42 00:02:14,110 --> 00:02:17,313 And therefore we get exactly that error here. 43 00:02:18,340 --> 00:02:21,500 So what we need to do is to call deposit 44 00:02:21,500 --> 00:02:23,730 actually on an account. 45 00:02:23,730 --> 00:02:27,680 And so what we want is for the result of this year 46 00:02:27,680 --> 00:02:30,380 to be again the account, 47 00:02:30,380 --> 00:02:31,430 right? 48 00:02:31,430 --> 00:02:32,653 And so let's do that. 49 00:02:34,150 --> 00:02:38,120 So all we have to do is return... 50 00:02:38,120 --> 00:02:39,350 this. 51 00:02:39,350 --> 00:02:41,833 Because this is of course, the current object. 52 00:02:42,980 --> 00:02:46,163 And now we do the same on all of them. 53 00:02:47,670 --> 00:02:48,503 Okay. 54 00:02:51,760 --> 00:02:53,023 And here the same. 55 00:02:54,520 --> 00:02:56,350 And that's it. 56 00:02:56,350 --> 00:02:57,890 So returning this 57 00:02:57,890 --> 00:03:00,930 will essentially make the method chainable. 58 00:03:00,930 --> 00:03:03,670 And this makes most sense, in methods 59 00:03:03,670 --> 00:03:06,360 that actually set some property. 60 00:03:06,360 --> 00:03:09,490 And so all of the three, that we just did this, 61 00:03:09,490 --> 00:03:11,130 actually do that. 62 00:03:11,130 --> 00:03:14,070 So this one sets the movements here. 63 00:03:14,070 --> 00:03:15,890 This one, actually two, 64 00:03:15,890 --> 00:03:18,763 and this one also changes the movement array. 65 00:03:19,610 --> 00:03:22,970 And so all of these, basically set some property. 66 00:03:22,970 --> 00:03:26,833 And so these are then very useful to make chainable. 67 00:03:28,010 --> 00:03:29,273 So let's see now. 68 00:03:30,660 --> 00:03:32,100 And... 69 00:03:32,100 --> 00:03:34,080 Well, we get no error, 70 00:03:34,080 --> 00:03:36,170 and we get loan approved. 71 00:03:36,170 --> 00:03:40,860 So that means that probably everything worked here. 72 00:03:40,860 --> 00:03:43,293 So let's take a look at our account here. 73 00:03:44,830 --> 00:03:47,483 Actually, let's call account getMovements. 74 00:03:49,600 --> 00:03:52,473 So that's why we have this method in the public API. 75 00:03:53,950 --> 00:03:57,090 And so indeed, all the deposits and withdrawals 76 00:03:57,090 --> 00:04:01,460 that we just did, are now in this Movements array. 77 00:04:01,460 --> 00:04:02,460 Great. 78 00:04:02,460 --> 00:04:06,940 So with this, you have yet another tool in your toolbox now. 79 00:04:06,940 --> 00:04:10,100 So experiment a little bit with this on your own. 80 00:04:10,100 --> 00:04:14,330 And maybe also when you start writing your own classes. 81 00:04:14,330 --> 00:04:15,220 All right. 82 00:04:15,220 --> 00:04:16,450 So with this one 83 00:04:16,450 --> 00:04:18,290 I actually showed you all there is 84 00:04:18,290 --> 00:04:22,960 to show about Object Oriented Programming in JavaScript. 85 00:04:22,960 --> 00:04:27,960 So what a long section here, but also a beautiful one, 86 00:04:28,240 --> 00:04:30,190 if you ask me. 87 00:04:30,190 --> 00:04:33,440 Now, just to really wrap up this section. 88 00:04:33,440 --> 00:04:38,270 Next up, I have a nice overview of the entire class syntax 89 00:04:38,270 --> 00:04:40,633 and then one final coding challenge.