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All right.
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So I've spoken so much about how awesome it is. How can we get it and incorporate jQuery into our
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web sites to start benefiting from all of its awesomeness?
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Well if you head over to jquery.com, you can see that, just like Bootstrap, you can download all the
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jQuery code files through their download page, or you can simply use a CDN.
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Now previously we explained what CDNs, or Content Delivery Networks, were and how they work.
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So if you're at all confused about this then take a look back at the Bootstrap module when we talked
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about this in detail.
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Now the most popular option across the web is to use Google's CDN.
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And, as we mentioned before, the beauty of using a popular CDN is that if a user has been to another web
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site that uses the same CDN to fetch the jQuery library, then they'll likely have it already cached
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and saved in their browser, which means that when they want to load up your web site they won't have
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to fetch a fresh copy of jQuery,
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they've already got it loaded and ready to go,
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giving your web site a much faster load rate. So we're going to be using the latest version of jQuery,
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3.3.1.
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Now at the time when you're watching this video it might just be that it'll be 3.3.2 or a larger
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number,
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but I want you to get the latest version with the script tag,
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and we're going to copy it and we're going to create a new project.
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Now I want you to go into your Web Development project folder and create a new project, and we're going
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to call this jQuery, and then we're going to drag and drop this into Atom, and then we're going to
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hit a in order to create a new file,
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and this is going to be index.html
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as well as styles.css and also our index.js.
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All right. So we've got all three files lined up and now let's head into our HTML, put in our boiler plate,
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and we're simply going to call our web site title just jQuery.
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We're going to hit save,
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and now I want you to pause the video and incorporate our CSS as well as Javascript into this HTML web
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page.
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So pause the video now and see if you remember how and where to do that.
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As we said before our style sheets should go into the head section of our web page.
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So in here just below the title I'm going to create a link that has a relationship of stylesheet, and
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the href is going to be styles.css.
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Now let's hit save and let's just test this to make sure that it's definitely working.
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So we're just going to change the background color of our body to red.
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And now if I copy the full path of my index.html and paste it in here,
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there we go.
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All right. So our CSS is working and linked up, next step is to include and link up our Javascript.
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Now if you completed the last module then you would know that,
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preferably, you should include your Javascript at the end of your web site just before the closing tag
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of the body.
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So over here we're going to include a script with an external source and the source is going to be index.js.
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I'm going to hit save.
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And we're going to include some Javascript code in here just to check that it's working,
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and if so we'll just send an alert that says "Working".
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So now if I hit refresh and I get an alert as well as my background being red,
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so I know that everything is all linked up and I can safely delete these bits of code.
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Now in our index.html I'm going to include a number of HTML elements.
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So first I'm going to have an h1 that just says Hello.
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And then I'm going to have a whole bunch of buttons and the buttons are just going to say Click Me, but
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I'm going to copy this and paste it so that we have five buttons in total as well as an h1.
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All right. So now let's hit save and I'm going to use the same code that I showed you in the last lesson
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to write some jQuery
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that's going to change the text color of each one to red.
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So we're going to start off with the dollar sign which is short for jQuery, so you can either write
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it like this or you can write it like this.
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They both do exactly the same thing in jQuery. Almost everybody will be using the dollar sign, as a lot
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of the reason why we're using jQuery is to shorten our code and do less typing.
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OK. So I'm going to target the h1 in our document and I'm going to change its
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CSS, namely the color property, to red.
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All right. So now we've got our jQuery code.
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We're going to be going through all of this code much much deeper later on.
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But now all you need to know is that we're using this to select the h1 on our web page and we're changing
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its
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CSS, namely the color property, to red.
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If I refresh my web site you'll see that nothing has happened because we need to incorporate jQuery
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in order for this to be valid because right now if you open up the console you can see that it's telling
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you that the dollar sign is not defined on Javascript line number two.
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Now that's because the dollar sign, if you remember, is jQuery,
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so if we don't have any jQuery then it's not really going to work.
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So let's incorporate it.
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Now head back to the Google Hosted Libraries page and copy the script tag,
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and we're going to paste that above our Javascript script tag.
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And now if you hit save and refresh then you can see that we have no more errors in our console and
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the text is now being turned red using our jQuery code inside our index.js.
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Now the position where you place your jQuery script tag is really important.
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For example, if we placed it below our index.js, then you'll see that it no longer works,
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and it no longer colors our text red, and we get the same problem that the dollar sign is not defined
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in our index.js on line 2.
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Now the reason is because if you remember the browser will read the code from top to bottom and the
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first thing that it will try to process is are index.js.
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So it heads over here,
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and it tries to make sense and carry out the instructions in here, and when it sees that dollar sign at
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this point it hasn't got a hold of the jQuery library yet,
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so it still doesn't know what this dollar sign and all the short code is all about.
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So that's why if you're going to use jQuery inside your Javascript code, then make sure that you
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place the script tag above it so that by the time it gets into this file,
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it already knows what the dollar sign is and how all of these shortening methods work.
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Now the other way that it might mess up is that if you had both of the script tags inside the head section
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of your web site, then when you refreshed your web site you'll notice that again it doesn't work.
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And in this case it's not even giving you a proper error. And you have to be really careful about including
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the CDN for our jQuery library in the head section of your web site, because what might happen is that
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before we've actually finished loading up the entire jQuery library, our index.js might already be
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trying to access it.
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So one of the ways that you can safeguard against this is to check whether if our jQuery library is ready,
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and we do that by using the dollar sign to select our document and then we use the ready method and
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we have a callback function in here.
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And that means that once our document is ready then it's going to call this code.
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So now if we hit save and we refresh then you can see our code now works because we waited until our
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jQuery library has finished loading and then we access the h1 to change its color.
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Now when you come across web sites, you'll often see this line of code.
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But another way of doing exactly the same thing is simply to include all scripts at the end of our web
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site right before the closing body tag.
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And this is exactly the same thing as this line of code.
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So when you see me writing jQuery code in the coming lessons, then you'll notice that I don't use
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that ready method because I always have my jQuery script at the end of my web site, and that way I only
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try to tap into and manipulate my HTML element after they've been loaded up and rendered on screen.
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