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jQuery's CSS functions provide easy cross-browser access for setting properties as well as working with positioning and sizing information for elements that are in your webpage. The CSS function allows you to retrieve and set styles for a set of matched elements, and up until now throughout this title you've probably been seeing me use that CSS function to make some of the early examples in this course visible to you to on the screen. So we are going to take a few moments and learn what it actually does.
So it has a few different forms. The first and simplest form is this one right here, CSS, and you give it a named property. This will return the value of the named, right here, CSS property for first matched element that you specify here in the result set that you are calling this on. The next version right here is CSS with the properties argument. This will set the CSS properties of every matched element in the result set using in object notation syntax, and this is very similar the attribute example that we saw earlier.
You can see here is an example of just creating an object that has a couple of properties and values to go with each one and then calling the CSS function with that object to set the properties on the results of a jQuery expression. But if all you want to do is set a single style property to a value on all of the matched elements, you can do that right here. This simply takes the name of a property like width or height or opacity or whatever, and sets it to whatever value you give it. Now if you just provide a number here rather than string, it's going to be converted automatically into a pixel value, except for certain CSS properties, and you can see those listed here like z-index, or font-weight, or opacity, or zoom, or the line-height.
Those do not take pixel values. So that won't happen there. jQuery also provides a set of functions for working with CSS classes. Again, this is used very commonly in things like animation or interactivity. You are setting styles on elements and taking them off and jQuery provides functions for adding and removing, toggling, and detecting these classes. You can see those in this table. So as you might expect the addClass will add a class or classes to each one of the matched elements.
The hasClass function will return true, if the specified class is present on at least one of the elements that are in the result set that you are calling this on. The removeClass is the opposite of addClass. It just simply takes that class off from all the matched elements. Then there is the toggle function. So the toggleClass will add this class if it's not there already and it will remove it, if it is present. You can also call it with switch. You can say hey, add it if the switch is true or remove it if the switch is false.
So moving on, let's take a look at the positioning functions. So CSS positioning functions provide a cross-browser way of figuring out where elements are on the page. There is a variety of functions for this. So the offset function gets the current offset. This comes back within object that has a top and a left. So same thing here. This is the offsetParent. It figures out the position parent of the first matched element in the result set. Position also comes back with a point, a top and the left. This gets the top and left position of an element relative to the parent that it's inside of.
Then the rest of the functions deal with scrolling. So for example this scrollTop will either get or set the scrollTop offset of either the first matched element in the case of getting it or you can set the scrollTop offset for all the matched elements in a result set, and the same thing for the left. Then finally the CSS sizing information. You can figure out how big elements are by using a variety of functions that jQuery gives you, and again these work across browsers. So the height functions will either get the current computed at by the browser pixel height of the first matched element in the set or you can set the height of all the matched elements.
Same thing for width. You get the current width as it's been computed by the browser or you can set the width. The innerHeight and innerWidth will, for example, get the inner height and that means excluding the border, but including the padding for the first matched element. The same thing for innerWidth. This will figure out how wide something is, but again excluding the border and including the padding. Then outerHeight and outerWidth work just the opposite. They will get the outer height, which includes the border and padding by default for the first matched element.
If you pass true for the margin, then the margin values are also included. The same thing for outerWidth. It will get the outer width as it's been computed by the browser and again you can ask to have the margin included. So that's a lot to digest. Let's take a look at some of these functions in action. So in the exercise folder, I have a file right here called css_sizing and I am just going to bring this up in the browser, so you can see what's happening. So you can see that we have a div here on the page and I am using some jQuery to compute various pieces of information about this object.
So you can see I have got the Height and Width here and the innerHeight and innerWidth, and the outerHeight and outerWidth and the offset and the position in the page. So what I want to do now is go back to file system and bring this up in Firefox. What you are going to see is that when Firefox comes up, and let me unmagnify this and move it over. You can see the values are pretty much the same for both browsers. They are both 180, they are both 250. You can see down here as well that the offset here is a little bit different for the offset and position.
So let's go into the code and see that. The position is being calculated by the position and the offset is being calculated by the offset. Now the offsets, remember, are a little bit different for each one of those guys. The top and left relative to the document. So here what we were doing is here are all of the spans. We are calling each one of these functions. So for the height, I am calling the height function, the width function, and you can see here when the results are filled out that that's where the values all go and you can see that that's how the browser is measuring each one of these guys.
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