Our users can add names to the list, remove them, 0:00 check them off when they responded, and edit them. 0:03 Now let's give users a way to filter the guest list, so 0:06 they can see everyone who has responded at a glance. 0:09 We'll create a checkbox above the list to toggle this feature on and off. 0:12 When the box is checked, we'll hide the guests who haven't yet responded and 0:17 display only those who have. 0:21 And when the box is unchecked, all invitees will be visible in the list. 0:23 So first, let's add a checkbox to the page, but rather than editing 0:29 index.html, let's add a checkbox and its behavior with JavaScript. 0:33 Apart from a checkbox, 0:38 we'll want to add a label to let users know what the checkbox is for. 0:40 And we can do this with a label element. 0:44 We'll place the label and checkbox in a div and append that to the page. 0:46 So to plan where we want to put the div let's take a look at index.HTML. 0:51 And looking at the code, 0:56 it looks like the best place to add the div is just before the UL element. 0:58 So let's go into app.js. 1:04 And at the top create the three elements 1:06 we want to use we'll create the div, 1:11 first with const div = document.createElement div, 1:16 then we'll create the label. 1:23 Let's call it filterLabel. 1:27 And we'll create the checkbox. 1:40 We'll call this one filterCheckbox. 1:43 Next under this we want to set the labels text content to hide those 1:58 who haven't responded. 2:03 So we'll type filterLabel.textContent. 2:05 And since this string has an apostrophe in it. 2:11 I'll switch over to using double quotes so inside the quotes. 2:14 I'll type hide those who haven't responded. 2:18 And now we'll set the input's type to checkbox with 2:25 filterCheckBox.type = checkbox, 2:30 And then we'll append the two elements the label and checkbox to the div. 2:37 So first we'll say div.appendChild filterLabel. 2:42 Then div.appendChild Filter checkbox. 2:51 Next, to insert this new div above the UL, we'll need to call insert before 2:58 on the parent of the UL which is the div with the class main. 3:04 Now we don't have a reference to the main development yet. 3:10 So let's select it. 3:13 Now the main div sits under the form in the DOM. 3:15 So I'll place it below the form and above the UL. 3:19 And now we can insert the div we built 3:38 into the DOM with mainDiv.insertBefore. 3:44 And we'll want to insert the div before the UL so we'll pass div first then UL. 3:51 So let's save our changes. 3:57 And go over to the browser and refresh and 3:59 you should see the check-box we just added. 4:02 Now it's there but it doesn't do anything yet. 4:04 So for example I'll add a name to the list and check the box and it doesn't hide it. 4:06 So let's fix that. 4:13 Back in app.js let's add an event handler to the checkbox. 4:15 Now we all ready have a reference to the checkbox here 4:20 in the filter checkbox constant. 4:23 So let's use this constant to call addEventListener on right 4:26 underneath where it was inserted into the DOM. 4:30 We'll say filterCheckBox.addEventListener. 4:34 Now check boxes trigger a change event so let's create a change event handler. 4:39 And here we want to know if the box is checked or 4:50 not which can be found in the checked property of the end put. 4:53 Remember at the end put is the target of the change event so 4:56 let's store its value in a constant called is checked. 5:00 If the box is checked, is checked will be true, and if not is checked will be false. 5:13 So now we'll need a reference to all the list items as 5:19 well because we'll be looping through them with this handler. 5:22 So we can traverse to them from the UL using the children property so 5:25 right below the constant. 5:29 We'll type const Lis ul.children. 5:31 Now if you haven't seen this before, 5:38 children provides a reference to a collection of elements children. 5:40 So next, if is checked is true, 5:46 we'll want to hide invitees that haven't responded yet. 5:49 And if it's false, we'll need to make sure all the invitees are displaying. 5:52 This sounds like a perfect case for an if statement. 5:56 So right below our constant, we'll write and if else. 5:58 Passing in is checked as the condition. 6:03 So now we also know that we'll need to go through all the list items in either case. 6:14 So let's set up for loops for both cases. 6:19 Now, we can go ahead and copy this for loop and paste it inside the else branch. 6:43 And now we'll also need to create a variable 6:51 to represent the individual allies inside each loop to make them more readable. 6:53 So first, we'll create a variable with let li = lists, 6:58 Then we can copy this variable and paste it inside the second for loop. 7:10 All right so now let's address the case where the filter is checked. 7:16 So we need to know whether the individual list items have been marked 7:21 responded or not. 7:24 Remember we're storing that information on the list items class attribute. 7:26 So we can check whether that class exists or not in an if statement. 7:30 So in the first for loop, we'll say if 7:34 Li.classname, === responded, 7:39 Run this code block, then else, run the code we include here. 7:47 And now we can hide an element by setting its CSS display property to none. 7:54 So in the else branch we'll type li style.display, = none. 8:00 And to show it again, we can set its display to an empty string. 8:09 So up here in the if branch, we'll say li.style.display = an empty string. 8:13 This will allow it to pick up its previous style. 8:22 So now let's move on to the case where we want to show all the guests whether 8:25 they've responded or not. 8:29 In this case we simply want to set every list items display property to an empty 8:31 string. 8:35 So in this bottom else branch, 8:37 we'll add li.styl.display = the empty string. 8:41 All right, so let's save our file and try this in the browser. 8:49 I'm going to refresh the page and enter a few names. 8:53 Let's say Elizabeth. 9:00 Andrew and Janice, I'll add a couple more let's say Gil and 9:03 Henry and then I'll just go through and check two names off. 9:09 And now when I check mark the new filter the unchecked names disappear. 9:16 And when I uncheck it, they show up again, perfect. 9:21 Our app now does everything we need it to do, 9:26 but there are still a few improvements we can make. 9:28 So far, we've been writing the app in a stream of consciousness way. 9:31 And this can really be useful for getting something up and running and 9:34 is often the approach developers use when they first write a program. 9:37 But once the basic functionality is in place you can often improve your programs 9:40 by looking at your code again. 9:44 And re factoring or changing your code, so that it still works the same but 9:46 it's easier to understand an update. 9:50