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jQuery

Name: jQuery
Uploaded: 2013-06-17T20:40:43Z
Duration: 677 s
Description: In this chapter, we'll write some jQuery that will increase the robustness of our CSS.

11:17 with Nick Pettit

In this chapter, we'll write some jQuery that will increase the robustness of our CSS.

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[jQuery] 0:00

[?music?] 0:04

[My Photos] 0:10

[Nick Pettit] We've modified the markup so that it's a little bit more flexible. 0:12

We can now go ahead and add more photos if we want to 0:15

to our gallery, so I'll just go ahead and copy and paste a few of them here, 0:20

and when we refresh the page here, 0:24

you can see that our stage dynamically resizes 0:27

and we have additional photos there. 0:30

However you can see that our gallery, 0:34

without using jQuery, is actually pretty broken right now, 0:36

so let's see what we can do to fix that. 0:39

So we'll switch back to our text editor 0:42

and we'll just go ahead and delete those two photos that we added 0:45

and refresh the page--there we go--back to normal, 0:49

and let's switch over to application.js. 0:52

So just to review our strategy here, we have placeholder list items 0:56

and those are floated. 1:01

Inside of those placeholders, we have our photos, 1:04

which will be absolutely positioned. 1:07

We'll do that with jQuery. 1:09

The reason that we have those placeholders is so that when a photo enlarges, 1:11

we can maintain the flow of the page. 1:16

If we were to just float those images and then apply the class large_photo, 1:19

we would actually be taking them out of the flow 1:23

and all of the photos would reflow on the page. 1:26

That's bad, so that's why we have those placeholders there. 1:29

Now, we'll use jQuery to set the positioning on our photos 1:32

and maintain the flow of the page. 1:37

So first thing's first--this selector image is way too generalized, 1:39

so let's go ahead and improve that. 1:44

We want to select images on the page--yes, but we want to select images 1:47

that have the class that contains the word photo. [class"=photo"] --just like that. 1:52

And then, we'll skip down here and we want to add in a variable called is_photo 2:00

and this will just detect whether or not we have a photo here. 2:07

Various is_photo = $(this).hasClass("photo"); 2:15

Go ahead and do that. 2:17

So then we can say that if this is a photo that we're in fact clicking on, 2:19

if (is_photo) { 2:26

then we can go ahead and toggle this class between photo and large_photo, 2:28

just like that. 2:34

Now, because our photos will not initially be absolutely positioned 2:38

but our large_photo is absolutely positioned, 2:42

at this point, we actually need to set the left and top offset 2:45

for our large_photo. 2:49

So let's go ahead and use the CSS method, 2:51

and inside of that, we'll give it the property ({"left": 2:55

with a value of 200 pixels 3:02

and then the value of "top": with 0 pixels. 3:05

And then, we'll go ahead and switch back to our CSS 3:12

and we can go ahead and remove top and left there, 3:15

just like that. 3:20

So the next thing we need to do is we need to grab the margin_left 3:22

and margin_top for our images, 3:27

because this is something that we're going to be using quite a bit. 3:31

So just after our function here, 3:34

we'll go ahead and say var margin_left as a variable, 3:37

and we're going to parse an integer here 3:42

because we don't want the pixel value--we want just the numerical value. 3:45

Then we'll go ahead and select our image 3:51

with the class that contains the string "photo" 3:58

and we actually want the parent of that, 4:04

which would be the placeholder. 4:09

.parent().css 4:11

and we want to grab the "marginLeft" property, 4:15

and in this case, I am using the JavaScript notation, not the CSS property-- 4:20

and we want to use a base 10 numbering system there, 4:29

which is that last value. 4:33

Next, we want to set a second variable, which is very similar to this one. 4:36

So we'll put a comma there, and we'll tab over, and this time, 4:42

instead of margin_left, we actually want to grab margin_top. 4:46

So we'll go ahead and change left to top there, 4:51

and then we need to do it for this value here ("marginTop") 4:56

and there we go. 5:04

Now, this will make our calculations a lot easier. 5:06

So the next thing we need to do 5:09

is when the page loads, we need to set the initial absolute positions on the images 5:11

relative to their parent containers. 5:17

So here's the secret: 5:20

the images will still be absolutely positioned, 5:22

but they will absoutely positioned when the page loads, 5:25

so you don't have to do the manual work of absolutely positioning them in the CSS. 5:29

So let's go ahead and do that. 5:34

In order to do this for each image, we need to again use this same selector $('img') 5:39

All of the images on the page that have the class name that contains the string "photo" 5:46

and then we're going to go through each one of them. 5:54

On each one, we're going to execute a function 5:58

and we're looping through each one, so we'll pass (index) to that function 6:03

and we'll put a ; there. 6:09

And first, we need to grab the position of the parent, 6:12

so we'll say =$(this).parent().position(); 6:19

And now, we can go ahead and use our margin_left, margin_top, 6:32

and position variables to set the absolute position on all of our images. 6:37

So we'll say $(this) and we'll set the css on each one of them, 6:41

and we'll say "position": "absolute", 6:48

"left" will be position.left + margin_left, 6:55

and then "top": will be position.top--this is the actual position of the photo-- 7:05

position.top + margin_top for our placeholder, just like that, 7:12

and we'll put a ; there so that's ready to go. 7:19

So let's go ahead and switch over to the browser and refresh the page 7:25

just to see how we're doing. 7:28

So now, when we click each one of these, 7:30

they will actually enlarge because the position is being set to absolute 7:32

and the large_photo class is set to absolute. 7:37

The problem is we can't click on our large photo 7:41

to set it back to its original position. 7:44

So let's go ahead and refresh the page, 7:47

and we'll go back to our text editor and we'll see if we can't fix that behavior. 7:50

So just before this if statement, I'm going to make a call to a function 7:55

that doesn't actually exist yet; we're going to write this function. 8:01

No matter what, we want to remove_large_photo() 8:05

whenever a photo is clicked on. 8:10

If we click on the large photo, we want that photo to become smaller. 8:13

If we have a large photo already and we click on another photo in the gallery, 8:17

we want the large photo to become smaller 8:22

and the photo we clicked on to become the new large photo. 8:25

So no matter what, 8:28

we want the large photo to be removed--no matter what we cilck on. 8:30

So we're calling the remove_large_photo(); function 8:34

and then, we get to actually write that function, 8:38

so let's go ahead and do that. 8:42

So we'll type function remove_large_photo() { 8:44

and we'll say if this is a large photo if ($("".large_photo")) 8:54

and then we use .length to determine if a large photo exists, 9:05

then, we want to get the var position 9:11

of our large_photo placeholder, 9:20

so the placeholder would be the parent of the large photo. 9:28

And then, of course, we want to get its position, just like that. 9:32

So we've stored the position of the placeholder for our large_photo. 9:38

And now, we want to select our large_photo 9:42

and we want to toggle the class large_photo and photo, 9:49

and that will basically just switch them out. 9:57

And then, we also need to reset the left and top offsets, 10:01

so let's go ahead and do that. 10:06

So we'll use the CSS method 10:08

and we already have all of the values we need, so we'll just say 10:12

"left": position.left + margin_left, 10:16

and again, this is the position of the actual photo plus the position of the placeholder. 10:24

So then we'll sync "top": position.top + margin_top 10:31

just like that, and we'll put a ; there. 10:41

And so now, when we switch back to the browser and refresh, 10:46

we can click on these photos, 10:49

and when we click on the large photo, it will become smaller again. 10:52

And then, when we click on a large photo and then click on another photo in the gallery, 10:56

the large photo will become smaller 11:00

and the photo we clicked on will become the new large photo, 11:03

so I'll show you that again. 11:06

When we click on one of the photos in the gallery, 11:08

the large photo will become small, 11:10

and the photo we clicked on will become the new large photo, just like that. 11:12

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