Do you want to write powerful, maintainable, and testable front end applications faster and with less code? Then consider joining this course to gain skills in one of the most popular Single Page Application (SPA) frameworks today, AngularJS. Developed and backed by Google, AngularJS is a very marketable skill to acquire. In this course, we will explore the core design of AngularJS 1.x (latest version of AngularJS 1), its components and code organization techniques. We will enhance the functionality of our web app by utilizing dependency injection to reuse existing services as well as write our own. We will create reusable HTML components that take advantage of AngularJS data binding as well as extend HTML syntax with a very powerful feature of AngularJS called directives. We’ll set up routing so our SPA can have multiple views. We will also learn how to unit test our functionality. At the end of this course, you will build a fully functional, well organized and tested web application using AngularJS and deploy it to the cloud.
Lecture 30, Part 2: Directive APIs and “&”
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Del curso dictado por Johns Hopkins University
Single Page Web Applications with AngularJS
1429 calificaciones
Johns Hopkins University
1429 calificaciones
Curso 5 de 6 en SpecializationRuby on Rails Web Development
De la lección
Week 3 - Promises, Ajax, and Custom Directives
Welcome to module 3! In this module, we go over a lot of essential features of AngularJS. We will start with learning about the Promise API. While Promises are essential to Angular, this topic reaches far beyond Angular. It's really an essential topic to understanding modern web development with Javascript. We will also learn about making calls to the server through the built in Angular service called the HTTP service. We'll finish off the module by spending a considerable amount of time on THE crown feature of AngularJS: directives. Directives are really at the core of the entire framework. They not only allow us to extend the functionality of existing HTML elements, which is already pretty amazing in an of itself, but they also allow us to create our own element with custom view and custom behavior. Pretty exciting stuff!
Conoce a los instructores
Yaakov ChaikinAdjunct Professor, Graduate Computer Science
Whiting School of Engineering
[MUSIC]
Okay, so back in our code editor and I'm located in Lecture30 folder,
which is located in fullstack-course5/examples folder.
And this is again, our shopping list directive app.
And the goal of task right now is to provide a button
next to each list item and let the user click it and it will get removed.
Except we'll going to try to accomplish this task
in a little bit of a wrong way first.
And what were going to do is,
we're going to supply this bad-remove attribute on our shopping list directive.
And we're going to pass the actual function directly as a reference
to our directive.
If we go to ab.gs, we'll see here that on our directive itself we're
going to create a badRemove property, and we're going to use an equal sign.
So it will be a bidirectional binding, and the function value of that remove
that we're going to pass in is going to be equal to this badRemove property.
In the actual service remove method, or controller I should say.
In the actual controller remove method we're going to have one more thing.
Let me actually close to see but what we're going to do is we're going to have
one more side effect here along comment and we're going to create a property under
this keyword which means since we're using control s syntax is gong to be attached to
the controllers instance and it's going to be called lastRemoved.
Basically whenever somebody passes as an itemIndex
we're going to look that itemIndex up in our this.items array, and
save the name of that item in the lastRemoved property.
In the index.html we're going to place a real quick span here,
and we'll say, Last or list.lastRemoved.
So now we're going to output whatever it is that is last removed
right inside of our controller.
This list is the label for our shopping list controller.
If we go to the shoppinglist.html which is the template for our directive,
we're going to see here a button and the button says, list.badRemoved.
And badRemoved is our function and
we're able to obviously take a function reference which is what this is.
Surrounded with parenths and execute it, passing it our dollar sign,
did the index switches the index in the list that somebody's clicking to remove
and the button name is going to be Bad Remove.
Just to look back at index.html we have our badRemove
Attribute map to list.remove items.
So it's the removeItem function value that is being assigned to this badRemove and
then that badRemoved gets called right here inside of our directive template.
Okay, let's save that.
And let's go to the browser and let's try to add item test 1.
We'll just say test for now, we'll click that item,
we'll see the Bad Remove button.
Test 2 click add item button, test 3 and click the add item button.
One more thing let's go take a look at when we go to the code
is that I printed out this console.log.
This is, and I'm printing out what the this variable is pointing to.
Just as important, so we'll be able to look at the console and
see when we attach the this.lastRemoved and
this.title, where is this actually pointing to at the time that we call it?
Let's go back to our browser and let's go ahead and
actually open the console so we could see what's going on.
Open the console here and let's go ahead and
try to click bad remove item number one.
When we click here we see that for some reason we
don't have any kind of announcement here what the last removed item was.
If we take a look at our console I think it's going to give us a clue.
This is, and remember this right now is being called from the remove item
method that is sitting on our controller that is the main controller and
if we take a look this is ShoppingListDirectiveController.
So it's not the shopping list controller,
it's shopping list directed controller which is not what we want because.
Because ShoppingListDirectiveController is the controller for our isolate scope and
we wanted this to execute in the parent controller's scope.
As you could see,
all these things that we thought were being assigned on the parent controller
scope are actually being assigned directly to our directives isolate scope.
And that's why you see that the title still says
list number 1 has 3 items in it, and so what happened to the title?
Well, when we said this.title and updated of the title with two items, it when had
and created that title, the title property on our ShoppingListDirectiveController.
Meanwhile the actual shopping list controller
doesn't know anything about this.
Let's go back to the code editor and
actually take a look as to why something like that is happening.
I actually created this this.html and it's just referencing this.js so
we will be able to see what's going on.
And here's a quick example on the microcosm as to what's going on
here in our controllers.
Suppose we have this function called Person and it says,
this.fullName is Yaakov, this.fav is Cookies.
And we have one method on the subject, which is the function and now what it's
doing is loading to the console and says, this.fullName likes this.fav.
If we now go ahead and create this yaakov object with the called the new person,
as we should,
that this variable inside of this object will be pointing to the person object.
And when we call yakov.describe,
in other words this method, this will still be pointing to the Person object,
and therefore, you'll be able to reference fullName and fave.
So let's go ahead and actually comment this out, for a second.
Let's go ahead and save that, and let's open this.html in the browser.
And you'll see that the console says, Yaakov likes cookies, very true.
Now if we go back, and go to this.js, what we're going to do now is we're going to
pull out the method from this yaakov object.
After all, yaakov.describe without the parenths is just a function value, so
we could grab that value and stick it in a local variable.
And then since that local variable is pointing to a function value,
we can actually execute it just by putting parenths behind it.
If we save that and go back to our browser, let's refresh that.
You can see it already says that undefined likes undefined.
How come this is going on?
Well, the reason this is going on is if we actually put a console.log right inside of
here, let's put a log statement here and say, what exactly is this variable?
Let's go ahead and say, this is, what is the this variable?
Let's go ahead and output this.
You could see that the first time we go around, this variable is the person but
the second time going around, this variable is actually the window.
And the window doesn’t have a full name and a fav.
The reason this is happening is because we took that method out of its context and
its context became the window,
because we were sitting after all in the global scope.
There is actually a java script solution to that and it's called the call method.
If you take the method that is out of context, in other words,
the this very well is pointing to whatever the surrounding context is.
You could actually give it context and basically it will get that
this variable assigned to whatever object that you're passing it in the call method.
So if we invoke describe with the call method and pass it to object yaakov then
this variable will all of a sudden once again be pointing to yaakov.
So if we save that and go back to our browser you'll see that even
though the first time it says undefined undefined the next time this is is
actually pointing back into Person and it actually will say, Yaakov likes cookies.
And this is what's happening in our controller.
If we go back,
we could close this now, what's happening in our controllers is that when this call
is being made right here, this call is being made just with a function reference.
It's like a variable that was yanked out of its context and
now sitting in a different context, in the case of the describe function
in our this example, it was sitting in the context of the window object.
Well, in the case of this badRemove example, it's sitting in the context
of the directives controller, not of the parent controller as we want it.
So the solution is, is to use the app reference and then pass a map
of arguments that is mapped to how we code this method, to begin with.
So let's go to app.gs and
what we're going to do now is we're going to declare yet another attribute.
And another attribute will be called onRemove.
And onRemove is going to have an ampersand binding
which means it's going to be a reference binding.
Will go to index.html and we'll add one more button here or
one more attribute and we'll call it on-remove and this time we'll call
list.remove item and will pass it in index.
Except as I told you as you remember
this index is not something that the ShoppingListController will be passing.
This index is just a key for our directive to be able to find and
assign some value to it so all of this will get executed in the context
of the ShoppingListController not of the ShoppingListDirectiveController.
Let's go ahead and actually put this back there.
It'll look a little bit better that way.
We'll go back to our shoppingList.html, that is the template for our directive.
Let's close the file browser so it'll be easier to see,
and we'll actually uncomment this button right here.
And if you take a look, it's list,
which is the list of my ShoppingListDirectiveController.
onRemove, that's the property we mapped on remove into the controller on our
Isolate Scope, and then you could see we're passing it an object that is a map.
It's mapping the index, if you take a look at the index.html,
this is the index that we're mapping.
So it's taking that index and
it's saying it should be equal to at the time you call this, it should be equal to
that'll assign index, which is the index through the loop at the moment.
Now when we save it and go back to the browser, we'll close our this example and
we'll close this as well.
And here is our directive with Isolate Scope, let's go ahead and add test,
well first of all it's not refreshing for some reason, let's refresh it, here we go.
Okay, so let's add our test 1, add 1, so we have bad remove and
with remove item will do test 2, add Item and test 3 and add that item.
And let's go ahead try to caught Removed Item.
Let's say Remove Test 2.
Request Removed Test 2 you'll see that the last item remove showed up here
which means that property did show up In the parent controller.
And if we take a look, in our remove item method,
we logged what the variable this pointed to.
In this case, it's pointing to the ShoppingListController which is
exactly what we wanted.
We wanted to execute that method In the context of the ShoppingListController
which is the parent of our directive.
And if we take a look all the things that we need are here and
we see are here and we see the last little property is here and
the shopping list title also got updated to two and therefore it's right there.
If we remove it again, this time we remove number 1, so it's number 1 and so on.
So this is working.
So once again, what allowed us to be able to call this method
in the context of the parent of this directive is the reference
that we declared onRemove property, which is the ampersand that is
giving us a reference to the function such that it's going to get executed
in its parent environment evaluating all the properties like they should be.
Okay, so let's summarize.
The & binding allows us to execute an expression,
such as a function value in the context of the parent scope.
The way this is done is the following.
The parent template must declare an attribute providing the method reference
for the directive to call on the parent, and an argument keys for
directive to bind values to when it needs to pass the data from the isolate scope
back to the parent scope.
The directive on the other hand calls the referenced method and
also provides an object map of argument key to value pairs.
This allows the directive to pass data back to the parent from the isolate scope.
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