Lecture 60: Dynamically Loading Home View Content

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Из курса от партнера Johns Hopkins University

HTML, CSS, and Javascript for Web Developers

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Johns Hopkins University

HTML, CSS, and Javascript for Web Developers

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Курс 4 из 6 — Specialization Ruby on Rails Web Development

Do you realize that the only functionality of a web application that the user directly interacts with is through the web page? Implement it poorly and, to the user, the server-side becomes irrelevant! Today’s user expects a lot out of the web page: it has to load fast, expose the desired service, and be comfortable to view on all devices: from a desktop computers to tablets and mobile phones. In this course, we will learn the basic tools that every web page coder needs to know. We will start from the ground up by learning how to implement modern web pages with HTML and CSS. We will then advance to learning how to code our pages such that its components rearrange and resize themselves automatically based on the size of the user’s screen. You’ll be able to code up a web page that will be just as useful on a mobile phone as on a desktop computer. No “pinch and zoom” required! Last but certainly not least, we will get a thorough introduction to the most ubiquitous, popular, and incredibly powerful language of the web: Javascript. Using Javascript, you will be able to build a fully functional web application that utilizes Ajax to expose server-side functionality and data to the end user.

Из урока

Using Javascript to Build Web Applications

In this module, we are going to take all those newly learned Javascript language skills and learn how to utilize them within the context of a web page. We’ll start by learning how to properly manipulate the web page components using the Javascript Document Object Model API. We will then move on to learning one of the most popular ways of serving up data to a web site - Ajax. We'll learn about the protocol that the language of the web speaks in (HTTP), how to set up and handle Ajax requests and responses, as well as how to process JSON data. We'll finish the module by connecting our restaurant web site from Module 3 to a real backend service that will allow us to pull the data for the restaurant menu dynamically from the server without having to reload the entire page.

Lecture 59: Fixing Mobile Nav Menu Automatic Collapse6:58

Lecture 60: Dynamically Loading Home View Content9:19

Lecture 61, Part 1: Dynamically Loading Menu Categories View6:22

Lecture 61, Part 2: Dynamically Loading Menu Categories View10:46

Lecture 62: Dynamically Loading Single Category View13:26

Lecture 63: Changing 'active' Button Style Through Javascript6:00

Course Wrap-Up1:12

Познакомьтесь с преподавателями

Yaakov Chaikin
Adjunct Professor, Graduate Computer Science
Whiting School of Engineering

[MUSIC]

Okay, so in this lecture, we're ready to move on.

And our next task is to load this entire content.

This main content of the front page to load this whole content dynamically.

Now first of all, why do we want to do that?

The reason we want to do it is because we're trying to move towards what's called

an SPA, or SPA and stands for single page application.

So a single page web application.

And besides for being a pretty popular web coding technique nowadays,

since SPAs heavy rely on Ajax,

this whole content right here is going to be inserted dynamically.

But the rest of the content is going to stay.

So we're going to basically update the least amount of the page possible

to make it functional.

And that's very advantageous because obviously it's going to be faster and

also is not going to refresh the page for the user.

It's going to be a much, much nicer user experience.

So let's go ahead and go to our code editor.

And right now, we're located in Lecture60 in the after folder and

we're looking at index.html.

Well, for that purpose in order to make the entire content, the main content

the dynamic, we actually need to wipe it out and this is exactly what we did.

We don't have any more in the index.html the main content.

There's only just a placeholder for the main content with id main-content.

Now, where did all of that stuff go?

Well, we have a new folder here called snippets.

And if we open it up, there is a file called homesnippet.html.

So if we open that up,

the entire contents of our homepage are really contained right here.

So you can see there's our jumbo tron, home tiles and so on.

We did change a couple of links,

cause you notice the menu item here is no longer just a link,

it's actually a link to basically nowhere with an onclick event handler.

And we'll talk about that a little bit later, but

we just kind of prepped it for the next step.

because obviously we're going to have to display our menu category page and

then individual single category page and we're still going to have to do this,

using this spot technique or using Ajax.

That is, we'll need to take that content and dynamically insert it

into the index dot html right here at the place holder in the content.

But for this lecture all we need to do is figure out how to insert

the previous mint page content inside the main content placeholder.

Let's go to our script.gs, where I have prewritten some code, and

let's go over that.

So first of all, you could see this code up top.

This is what we just wrote in a previous lecture.

This is just to make the collapsible button

collapse the menu when it loses focus.

Okay, so what we're going to do is first of all we're going to set up

an immediately invoked functional expression.

As you can see here we're starting with prints global and going all the way down

here we're executing this function passing it to window object.

So our global right here Is really just the window object.

And we're setting up the namespace dc, just probably for David Chu's.

That's how I named it.

And as you could see,

we're exposing this thing right before the end of this call function.

We're saying global, which is really window.

.$dc, that's that where we want to expose this as and dc our internal theme space.

So whatever we attach to the dc as a property

is going to get exposed to the global object in order for

us to use it in some other page or some other script.

Okay, so let's take a look as to what we're doing here.

First of all we're setting up our home HTML.

That's nothing more than just the URL as to where the snippet is going to sit.

And then we're going to have a convenience method here so we don't have to write this

from scratch every time because we're going to have to do this several times.

Is if you give me a selector and you give me the HTML, I will go ahead and take,

select that selector.

Take that argument, take that element I should say, grab that element, the target

element, and set its inner HTML, to whatever the HTML string that you send me.

So this is just a convenience method to say, insertHtml, pass it a selector, and

the HTML string, and it will insert it into the target element.

Another function that we need is show loading icon, it's this showLoading here.

So obviously an HS request is going to be done asynchronously and

it will go out to the server and bring us back some content.

But meanwhile, what is going to be displayed to the user?

Well, we obviously don't want to display nothing.

We don't want to display blank.

We would rather display some sort of an animated icon that

is going to show the user that something is going on.

Well, ajax-loader.gif is an animated GIF.

And I'm going to tell you in a minute where I got that from.

But let me go over the code first.

So showLoading basically says give me a selector

to which I should attach this loading icon.

And I'm going to set up a very simple div.

I'm going to put an image inside of that div and close the div.

So this is just a, building up an HTML string.

And it's pointing to this images/ajax-loader.gif.

And then I'm reusing my insertHtml that I just defined, and

basically inserting that into this particular selector.

So I'm able to then display this.

Rotating or whatever it is Ajax loader icon inside this selective past send.

Now where did I get this index or ajax-loader.gif.

Let me go back to the browser for a second.

There's a great website called ajaxload.info and it allows you to

basically choose different types of loading icons that you could choose and

then set whatever background color you want and whatever foreground color

you want and generate that icon for yourself, and there it is.

And then you could click to download that GIF, and

then you could use it in your web site and absolutely free.

So it's a great web site for these type of activities.

But it's not the only one, there are others out there,

and definitely google for it and you'll see some others

that are perhaps a little bit more creative but not as straight forward.

So let's go back to our code editor, and keep going here, so.

So we want to set up an on-page load.

What we're doing here is we're waiting till the dom content has been loaded.

And in that case, once it is loaded, we're able to start executing things and

basically executing queries.

The selector quarries that will actually find things since we

need HTML to be loaded at that point in order to execute query selectors.

And here what we're about to do is we're about to make that Ajax call we've

seen before.

But before we make the Ajax call we want to go ahead and

turn on that showLoading.

And that showLoading is going to insert in the main Content ID that element

is going to insert our rotating Ajax loader so

it's going to place it right here as the inner HTML of this element.

Once it's done it's going to issue our ajax request.

The Ajax request is going to be a fairly simple one

it's going to give us the home URL or the home HTML URL.

And that's something we've defined right here, previously.

That's just the URL as to where that snippet is sitting.

And since we're passing false as the last argument, as you remember,

false means I don't want you to pre-process this as JSON.

And we don't want this as JSON, because, all it is is just an HTML snippet.

What is going to come back in our handler function

is just some text to actually just a response HTML.

And once it does come back we're going to select our element with ID main-content

and set its innerHTML to whatever the responseText came back to be.

And that's about it.

So once we're done with this, we can save this, go to our browser,

and switch to David Chu's China Bistro through our browser sync.

And we if we actually reload this right now, it should very quickly get loaded so

the entire content is here.

So let's actually take a look at The Chrome developer tools

to make sure that we think is going on is in fact going on.

Let's go ahead and open it up and leave it on XHR, which stands for

XMLHttpRequest that's the Ajax request, so we don't want to see all the requests.

We just want to see the Ajax only.

So let's go ahead and refresh the browser that's going to give us

a whole bunch of requests here because we have Google Maps embedded in as well.

So there's definitely a lot of things going on here.

But one of the things you see is there is an Ajax Request for home snippet.html.

And that's exactly what we get, we get that little snippet over here.

And that happens once the page loads and kicks off this whole Ajax process,

which then goes ahead and fills in the content, the main content of our page.

So if we take a look right now and try to click on this Menu button right here,

nothing's really going to happen, it's just going to sit right here.

But if we open the Chrome Developer Tools and look at our console,

we going to see there's an error, the dc.loadMenuCategories is not a function.

Well, that's true it's not a function because we haven't defined it yet.

That function is supposed to swap the content of our HTML page,

the main content, to the MenuCategoires content and

that's what we're going to do in the next lecture.

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