In this article, you will find answers to the top 50 interview questions and answers in AngularJS.
This article has become old as Angular 1.X is outdated. If you want to Learn Angular 2 or 4, you can start from this article. Learn Angular Step by step.
Contents
AngularJS is a JavaScript framework which simplifies binding JavaScript objects with HTML UI elements.
Let us try to understand the above definition with simple sample code.
Below is a simple Customer function with CustomerName property. We have also created an object called as Cust which is of Customer class type.
function Customer()
{
this.CustomerName = "AngularInterview";
}
var Cust = new Customer();
Now let us say the above customer object we want to bind to a HTML textbox called as TxtCustomerName. In other words, when we change something in the HTML text box, the customer object should get updated and when something is changed internally in the customer object, the UI should get updated.
<input type=text id="TxtCustomerName" onchange="UitoObject()"/>
So in order to achieve this communication between UI to object, developers end up writing functions as shown below. UitoObject function takes data from UI and sets it to the object while the other function ObjecttoUI takes data from the object and sets it to UI.
function UitoObject()
{
Cust.CustomerName = $("#TxtCustomerName").val();
}
function ObjecttoUi()
{
$("#TxtCustomerName").val(Cust.CustomerName);
}
So if we analyze the above code visually, it looks something as shown below. Both your functions are nothing but binding code logic which transfers data from UI to object and vice versa.
Now the same above code can be written in Angular as shown below. The JavaScript class is attached to a HTML parent div tag using ng-controller directive and the properties are binded directly to the text box using ng-model declarative.
So now whatever you type in the textbox updates the Customer object and when the Customer object gets updated, it also updates the UI.
<div ng-controller="Customer">
<input type=text id="txtCustomerName" ng-model="CustomerName"/>
</div>
In short, if you now analyze the above code visually, you end up with something as shown in the below figure. You have the VIEW which is in HTML, your MODEL objects which are JavaScript functions and the binding code in Angular.
Now that binding code have different vocabularies.
- Some developers called it
ViewModel because it connects the Model and the View . - Some call it
Presenter because this logic is nothing but presentation logic. - Some term it has
Controller because it controls how the view and the model will communicate.
To avoid this vocabulary confusion, the Angular team has termed this code as Whatever. It’s that Whatever code which binds the UI and the Model. That’s why you will hear lot of developers saying Angular implements MVW architecture.
Directives are attributes decorated on the HTML elements. All directives start with the word ng. As the name says directive, it directs Angular what to do.
For example, below is a simple ng-model directive which tells angular that the HTML textbox txtCustomerName has to be binded with the CustomerName property.
<input type=text id="txtCustomerName" ng-model="CustomerName"/>
Some of the most commonly used directives are ng-app,ng-controller and ng-repeat.
Controllers are simple JavaScript function which provides data and logic to HTML UI. As the name says controller, they control how data flows from the server to HTML UI.
For example, below is simple Customer controller which provides data via CustomerName and CustomerCode property and Add/ Update logic to save the data to database.
Note: Do not worry too much about the $scope, we will discuss the same in the next question. |
function Customer($scope)
{
$scope.CustomerName = "Shiv";
$scope.CustomerCode = "1001";
$scope.Add = function () {
}
$scope.Update = function () {
}
}
ng-controller is a directive. Controllers are attached to the HTML UI by using the ng-controller directive tag and the properties of the controller are attached by using ng-model directive. For example, below is a simple HTML UI which is attached to the Customer controller via the ng-controller directive and the properties are binded using ng-model directive.
<div ng-controller="Customer">
<input type=text id="CustomerName" ng-model="CustomerName"/><br />
<input type=text id="CustomerCode" ng-model="CustomerCode"/>
</div>
Angular expressions are unit of code which resolves to value. This code is written inside curly braces {.
Below are some examples of Angular expressions:
The below expression adds two constant values.
{{1+1}}
The below expression multiplies quantity and cost to get the total value.
The value total cost is {{ quantity * cost }}
The below expression displays a controller scoped variable.
<div ng-controller="CustomerVM">
The value of Customer code is {{CustomerCode}}
</div>
The value of Customer code is {{CustomerCode}}.
We can use ng-init directive to achieve the same. You can see in the below example we have used ng-init directive to initialize the pi value.
<body ng-app="myApp" ng-init="pi=3.14">
The value of pi is {{pi}}
</body>
$scope is an object instance of a controller. $scope object instance gets created when ng-controller directive is encountered.
For example, in the below code snippet, we have two controllers - Function1 and Function2. In both the controllers, we have a ControllerName variable.
function Function1($scope)
{
$scope.ControllerName = "Function1";
}
function Function2($scope)
{
$scope.ControllerName = "Function2";
}
Now to attach the above controllers to HTML UI, we need to use ng-controller directive. For instance, you can see in the below code snippet how ng-controller directive attaches function1 with div1 tag and function2 with div2 tag.
<div id="div1" ng-controller="Function1">
Instance of {{ControllerName}} created
</div>
<div id="div2" ng-controller="Function2">
Instance of {{ControllerName}} created
</div>
So this is what happens internally. Once the HTML DOM is created, Angular parser starts running on the DOM and following are the sequence of events:
- The parser first finds
ng-controller directive which is pointing to Function1. He creates a new instance of $scope object and connects to the div1 UI. - The parser then starts moving ahead and encounters one more
ng-controller directive which is pointing to Function2. He creates a new instance of $scope object and connects to the div2 UI.
Now once the instances are created, below is a graphical representation of the same. So the DIV1 HTML UI is binded with function1 $scope instance and the DIV2 HTML UI is binded with function2 $scope instance. In other words, now anything changes in the $scope object, the UI will be updated and any change in the UI will update the respective $scope object.
$rootScope is a parent object of all $scope angular objects created in a web page.
Let us understand how Angular does the same internally. Below is a simple Angular code which has multiple DIV tags and every tag is attached to a controller. So let us understand step by step how Angular will parse this and how the $rootScope and $scope hierarchy is created.
The Browser first loads the above HTML page and creates a DOM (Document Object Model) and Angular runs over the DOM. Below are the steps how Angular creates the rootscope and scope objects.
- Step 1: Angular parser first encounters the
ng-app directive and creates a $rootScope object in memory. - Step 2: Angular parser moves ahead and finds the expression
{{SomeValue}}. It creates a variable. - Step 3: Parser then finds the first
DIV tag with ng-controller directive which is pointing to Function1 controller. Looking at the ng-controller directive, it creates a $scope object instance for Function1 controller. This object it then attaches to $rootScope object. - Step 4: Step 3 is then repeated by the parser every time it finds a
ng-controller directive tag. Step 5 and Step 6 is the repetition of Step 3.
If you want to test the above fundamentals, you can run the below sample Angular code. In the below sample code, we have created controllers Function1 and Function2. We have two counter variables one at the root scope level and other at the local controller level.
<script language=javascript>
function Function1($scope, $rootScope)
{
$rootScope.Counter = (($rootScope.Counter || 0) + 1);
$scope.Counter = $rootScope.Counter;
$scope.ControllerName = "Function1";
}
function Function2($scope, $rootScope)
{
$rootScope.Counter = (($rootScope.Counter || 0) + 1);
$scope.ControllerName = "Function2";
}
var app = angular.module("myApp", []);
app.controller("Function1", Function1);
app.controller("Function2", Function2);
</script>
Below is the HTML code for the same. You can have attached Function1 and Function2 two times with ng-controller which means four instances will be created.
<body ng-app="myApp" id=1>
Global value is {{Counter}}<br />
<div ng-controller="Function1">
Child Instance of {{ControllerName}} created :- {{Counter}}
</div><br />
<div ng-controller="Function2">
Child Instance of {{ControllerName}} created :- {{Counter}}
</div><br />
<div ng-controller="Function1">
Child Instance of {{ControllerName}} created :- {{Counter}}
</div><br />
<div ng-controller="Function2">
Child Instance of {{ControllerName}} created :- {{Counter}}
</div><br />
</body>
Above is the output of the code you can see the global variable of root scope has be incremented four times because four instances of $scope have been created inside $rootScope object.
Angular is a MVW framework. It helps us to bind the model and the view. In other words, when any change happens in the model, the view gets updated. This updation of the model and the view is done by a loop called as digest cycle.
Digest cycle follows four important steps:
- Step 1: Some kind of event is triggered by the end user like typing (
onchange), button click, etc. and due to this activity model value changes. - Step 2: Angular first checks if the new value and old values are same. If they are the same, it does not do anything. If they are not, then it invokes the digest cycle.
- Step 3: Digest cycle then runs through the scope objects to check which objects are getting affected because of this change. Every object in the scope has watchers. Watchers as the name says listens to whether the model has changed or not. Digest cycle informs the watchers about the model change and then watchers synchronize the view with the model data.
- Step 4: In step 3, watchers update the view and due to that update, it's very much possible that the model changes again. Now due to this model change, we have to re-evaluate the view again. So the digest loop runs once again to ensure that all things are synched up. This second loop which runs is termed as dirty check loop.
Below is the figure wherein we have highlighted all the four steps.
So summarizing definitions for the above three concepts:
- Digest cycle: It is a simple loop which updates the model and view.
- Watchers: They are listeners which are attached to expression and angular directives and fire when the model data changes.
- Dirty check: This is a extra digest loop which runs to check any cascading left over updates due to the first digest cycle.
If there are a lot of unnecessary watchers, then digest cycle has to work harder. As per AngularJS team, having more than 2000 watchers on Angular screen is a bad practice.
Consider the below simple example where we have two ng-models and three expression. So in all, we should have 5 watchers for the below screen:
There are lot of great open source tools which help you to figure out the number of watchers, one such tool is the batarang tool. It’s a simple Google chrome extension which you can install separately.
Below is a simple snapshot wherein we ran the above program, pressed F12, enabled batarang and below are the results. You can see that he is showing 5 total watchers and for that digest cycle ran for 0.07 MS.
To decrease digest cycle time, you need to decrease the number of watchers. Below are some best practices you can follow to decrease number of watchers:
- Remove unnecessary watchers.
- Use one time Angular binding. Especially if you see
ng-repeat loop apply one time binding. - Work in batches.
- Cache DOM.
- Use Web worker.
Yes , you can force it to run manually by calling the $apply() method.
No, you do not need Jquery for Angular. It’s independent of Jquery.
It's two way binding. So whenever you make changes in one entity, the other entity also gets updated.
At the heart of Angular framework is a parser. A parser which parses the Angular directives and render’s HTML output.
Angular parser works in three steps:
Step 1: HTML browser parses the HTML and creates a DOM (Document Object Model).
Step 2: Angular framework runs over this DOM looks at the Angular directives and manipulates the DOM accordingly.
Step 3: This manipulated is then rendered as HTML in the browser.
Now the above Angular parsing is not so simple as it looks to be. It occurs in two phases Compile and Link. First, the compile phase occurs then the link phase.
In compile phase, the Angular parser starts parsing the DOM and whenever the parser encounters a directive, it creates a function. These functions are termed as template or compiled functions. In this phase, we do not have access to the $scope data.
In the link phase, the data i.e., ($scope) is attached to the template function and executed to get the final HTML output.
To make HTTP calls, we need to use the $http service of Angular. In order to use the http services, you need to provide the $http as a input in your function parameters as shown in the below code:
function CustomerController($scope,$http)
{
$scope.Add = function()
{
$http({ method: "GET", url: "http://localhost:8438/SomeMethod" }).success
(function (data, status, headers, config)
{
}
}
}
$http service API needs at least three things:
- First, what is the kind of call
POST or GET. - Second, the resource URL on which the action should happen.
- Third, we need to define the
success function which will be executed once we get the response from the server.
$http({ method: "GET", url: "http://localhost:8438/SomeMethod" }).success
(function (data, status, headers, config)
{
}
You need to pass data using the data keyword in the $http service API function. In the below code, you can see that we have created a JavaScript object myData with CustomerName property. This object is passed in the $http function using HTTP POST method.
Var myData = {};
myData.CustomerName = "Test";
$http({ method: "POST",
data: myData,
url: "http://www.xyz.com"})
.success(function (data, status, headers, config)
{
}
Dependency injection is a process where we inject the dependent objects rather than consumer creating the objects. DI is everywhere in Angular or we can go one step ahead and say Angular cannot work without DI.
For example in the below code, $scope and $http objects are created and injected by the Angular framework. The consumer, i.e., CustomerController does not create these objects himself rather Angular injects these objects.
function CustomerController($scope,$http)
{
}
There are two big benefits of DI: Decoupling and Testing.
Let’s first start with Decoupling. Consider your application has a logger functionality which helps to log errors, warning, etc. in some central place. This central place can be a file, event viewer, database, etc.
function FileLogger()
{
this.Log = function () {
alert("File logger");
};
}
function EventLogger()
{
this.Log = function () {
alert("Event viewer logger");
};
}
Now let’s say you have a Customer class that wants to use the Logger classes. Now which Logger class to use depends on configuration.
So the code of Customer is something as shown below. So depending on the configuration, Customer class either creates FileLogger or it creates EventLogger object.
function Customer($scope, Logger)
{
$scope.Logger = {};
if (config.Loggertype = "File")
{
$scope.Logger = new FileLogger();
}
else
{
$scope.Logger = new EventLogger();
}
}
But with DI, our code becomes something as shown below. The Customer class says he is not worried from where the Logger object comes and which type of Logger objects are needed .He just wants to use the Logger object.
function Customer($scope,$http, Logger)
{
$scope.Logger = Logger;
}
With this approach, when a new Logger object gets added, the Customer class does not have to worry about the new changes because the dependent objects are injected by some other system.
The second benefit of DI is testing. Let’s say you want to test the Customer class and you do not have internet connection. So your $http object method calls can throw errors. But now, you can mock a fake $http object and run your customer class offline without errors. The fake object is injected using DI.
Service helps to implement dependency injection. For instance, let’s say we have the below Customer class who needs Logger object. Now Logger object can be of FileLogger type or EventLogger type.
function Customer($scope,$http, Logger)
{
$scope.Logger = Logger;
}
So you can use the service method of the application and tie up the EventLogger object with the Logger input parameter of the Customer class.
var app = angular.module("myApp", []); // creating a APP
app.controller("Customer", Customer); // Registering the VM
app.service("Logger", EventLogger); // Injects a global Event logger object
So when the controller object is created, the EventLogger object is injected automatically in the controller class.
Angular Services create and inject global instances. For example, below is a simple HitCounter class which has a Hit function and this function increments the variable count internally every time you call hit the button.
function HitCounter()
{
var i = 0;
this.Hit = function ()
{
i++;
alert(i);
};
}
This HitCounter class object is injected in MyClass class as shown in the below code.
function MyClass($scope, HitCounter)
{
$scope.HitCounter = HitCounter;
}
Below code advises the Angular framework to inject HitCounter class instance in the MyClass class. Read the last line of the below code specially which says to inject the HitCounter instance.
var app = angular.module("myApp", []); // creating a APP
app.controller("MyClass", MyClass); // Registering the VM
app.service("HitCounter", HitCounter); // Injects the object
Now let’s say that the Controller MyClass is attached to two div tags as shown in the below figure.
So two instances of MyClass will be created. When the first instance of MyClass is created, a HitCounter object instance is created and injected in to MyClass first instance.
When the second instance of MyClass is created, the same HitCounter object instance is injected in to second instance of MyClass.
Again, I repeat the same instance is injected in to the second instance, new instances are not created.
If you execute the above code, you will see counter values getting incremented even if you are coming through different controller instances.
Factory in real world means a premise where products are manufactured. Let’s take an example of a computer manufacturing firm. Now the company produces different kinds and sizes of computers like laptops, desktops, tablets, etc.
Now the process of manufacturing the computer products are same with slight variation. To manufacture any computer, we need processor, RAM and hard disk. But depending on what kind of final case packing is the final product shapes.
That’s what the use of Factory in Angular.
For example, see the below code we have a Customer, Phone and Address class.
function Customer()
{
this.CustomerCode = "1001";
this.CustomerName = "Shiv";
}
function Phone()
{
this.PhoneNumber = "";
}
function Address()
{
this.Address1 = "";
this.Address2 = "";
}
So now we would create different types of Customer object types using the combination of Address and Phones object.
- We would like to combine
Customer with Address and create a Customer object which has Address collection inside it. - Or must be we would like to create
Customer object with Phone objects inside it. - Or must be
Customer object with both Phone and Address objects.
In other words, we would like to have different permutation and combination to create different types of Customer objects.
So let’s start from bottom. Let’s create two factory functions, one which creates Address object and the other which creates Phone objects.
functionCreateAddress()
{
var add = new Address();
return add;
}
functionCreatePhone()
{
var phone = new Phone();
return phone;
}
Now let’s create a main factory function which uses the above two small factory functions and gives us all the necessary permutation and combination.
In the below factory, you can see that we have three functions:
CreateWithAddress which creates Customer with Address objects inside it.CreateWithPhone which creates Customer object with Phone objects inside it.CreateWithPhoneAddress which creates Customer object with aggregated Phone and Address objects.
function CreateCustomer() {
return {
CreateWithAddress: function () {
varcust = new Customer();
cust.Address = CreateAddress();
returncust;
},
CreateWithPhone: function () {
varcust = new Customer();
cust.Phone = {};
cust.Phone = CreatePhone();
returncust;
}
,
CreateWithPhoneAddress: function () {
debugger;
varcust = new Customer();
cust.Phone = CreatePhone();
cust.Address = CreateAddress();
returncust;
}
}
}
Below is a simple CustomerController which takes CustomerFactory as the input. Depending on TypeOfCustomer, it creates with Address, Phones or both of them.
functionCustomerController($scope, Customerfactory)
{
$scope.Customer = {};
$scope.Init = function(TypeofCustomer)
{
if (TypeofCustomer == "1")
{
$scope.Customer = Customerfactory.CreateWithAddress();
}
if (TypeofCustomer == "2")
{
$scope.Customer = Customerfactory.CreateWithPhone();
}
if (TypeofCustomer == "3") {
$scope.Customer = Customerfactory.CreateWithPhoneAddress();
}
}
}
You also need to tell Angular that the CreateCustomer method needs to be passed in the input. For that, we need to call the Factory method and map the CreateCustomer method with the input parameter CustomerFactory for dependency injection.
var app = angular.module("myApp", []); // creating a APP
app.controller("CustomerController", CustomerController); // Register the VM
app.factory("Customerfactory", CreateCustomer);
So if we consume the CustomerController in UI, depending on the situation, it creates different flavors of Customer object. You can see in the below code we have three different DIV tags and depending on the TypeofCustomer we are displaying data.
Factory and Service are different ways of doing DI (Dependency injection) in Angular. Please read the previous question to understand what is DI.
So when we define DI using service as shown in the code below. This creates a new GLOBAL instance of the Logger object and injects it in to the function.
app.service("Logger", Logger); // Injects a global object
When you define DI using a factory it does not create a instance. It just passes the method and later the consumer internally has to make calls to the factory for object instances.
app.factory("Customerfactory", CreateCustomer);
Below is a simple image which shows visually how DI process for Service is different than Factory.
| | Factory | Service |
| Usage | When we want to create different types of objects depending on scenarios. For example, depending on scenario, we want to create a simple Customer object , or Customer with Address object or Customer with Phone object. See the previous question for more detailed understanding. | When we have utility or shared functions to be injected like Utility , Logger, Error handler, etc. |
| Instance | No Instance created. A method pointer is passed. | Global and Shared instance is created. |
Angular leverages HTML 5 validations and new form element types to implement validation.
For instance, below is a simple form which has two text boxes. We have used HTML 5 required validation attribute and a form element of type email.
<form name="frm1" id="frm1" >
Name :- <input type=text name="CustomerName" id="CustomerName" required />
Email :- <input type=email name="Email" id="Email" />
<input type=submit value="Click here"/>
</form>
Below are some examples of new form elements introduced in HTML 5 and Angular works with almost all of them:
- Color
- Date
- Datetime-local
- Email
- Time
- Url
- Range
- Telephone
- Number
- Search
When you run the above HTML inside a browser which understands HTML 5, you will see your validations and form types in actions as shown in the below browser screenshot.
Angular leverages HTML 5 validation attributes and new HTML 5 form elements. Now if we want Angular to handle validation, we need first stop HTML 5 to do validation. So for that, the first step is to specify novalidate attribute on the form tag.
<form name="frm1" novalidate>
-----
</form>
So now, the HTML will not fire those validations, it will be routed to the Angular engine to further take actions.
In other words, when end user fills data in the HTML UI, validation events are routed to Angular framework and depending on scenario Angular sets a field called as $Valid. So if the validations are fine, it sets it to True or else it sets it to False.
So you can see in the below code, we have attached the Angular controller and models to the text boxes. Watch the code of the button it has ng-disabled attribute which is set via the $Valid property in a NEGATED fashion.
Negated fashion means when there is no error it should enable the button and when there are errors that means it’s false, it should disable the button.
<form name="frm1" novalidate>
Name:-<input type=text ng-model="Customer.CustomerName" name="CustomerName" required />
Email :- <input type=email ng-model="Customer.Email" name="Email" />
<input type=submit value="Click here" ng-disabled="!(frm1.$valid)"/>
</form>
Note: Name is needed for the validations to work.
To check for a specific field, you need to use the below DOM code.
!frm1.CustomerName.$valid
SPA is a concept where rather loading pages from the server by doing postbacks we create a single shell page or master page and load the webpages inside that master page.
By using Angular routes.
Implementing Angular route is a five step process: -
Step 1: Add the Angular-route.js file to your view.
<script src="~/Scripts/angular-route.js"></script>
Step 2: Inject ngroute functionality while creating Angular app object.
var app = angular.module("myApp", ['ngRoute']);
Step 3: Configure the route provider.
In route provider, we need to define which URL pattern will load which view. For instance in the below code, we are saying Home loads Yoursite/Home view and Search loads YourSite/Search view.
app.config(['$routeProvider',
function ($routeProvider) {;
$routeProvider.
when('/Home, {
templateUrl: 'Yoursite/Home',
controller: 'HomeController'
}).
when('/Search', {
templateUrl: YourSite/Search',
controller: 'SearchController'
}).
otherwise({
redirectTo: '/'
});
}]);
Step 4: Define hyperlinks.
Define hyper link with the # structure as shown below. So now when user clicks on the below anchor hyperlinks, these actions are forwarded to route provider and router provider loads the view accordingly.
<div>
<a href="#/Home">Home</a><br />
<a href="#/Search"> Search </a><br />
</div>
Step 5: Define sections where to load the view.
Once the action comes to the router provider, it needs a place holder to load views. That’s defined by using the ng-view tag on a HTML element. You can see in the below code we have created a DIV tag with a place holder. So the view will load in this section.
<div ng-view>
</div>
So if we summarize angular routing is a three step process (Below is a visual diagram for the same): -
- Step 1: End user clicks on a hyperlink or button and generates action.
- Step 2: This action is routed to the route provider.
- Step 3: Router provider scans the URL and loads the view in the place holder defined by
ng-view attribute.
Angular UI route helps to implement SPA concept using the concept of STATES. The main goal of SPA is navigating from one view to other view without reloading the main page. Angular UI route visualizes every view as a STATE. When you want to navigate from one view to other view, you can either use the STATE names or use URL.
So let’s say we want to navigate from Home.htm view to About.htm view so we can define two states Home and About and link them to the respective HTML page as shown below.
You can also specify URL by which you can move between these states by using url property as shown in the below code.
myApp.config(function ($stateProvider, $urlRouterProvider) {
$stateProvider
.state('Home', {
url: '/HomePage',
templateUrl: 'Home.htm'
})
.state('About', {
url: '/About',
templateUrl: 'About.htm'
})};
Now once the states are defined to we need to use ui-sref and if you want to navigate using url provide url value in the href of the anchor tag.
We also need to provide "<ui-view>" tag to define in which location we want to load the views.
<a ui-sref="About" href="#About">Home</a>
<a href="#Home">About</a>
<ui-view></ui-view>
Below is the complete code if HTML, please ensure you have also referenced of Angular-UI js file. You can also see App.js file, this file has code which defines the states.
<script src="Scripts/angular.js" type="text/javascript"></script>
<script src="Scripts/angular-ui-router.js" type="text/javascript"></script>
<script src="Scripts/App.js" type="text/javascript"></script>
<body ng-app="myApp">
<a ui-sref="About" href="#About">Home</a>
<a href="#Home">About</a>
<ui-view></ui-view>
</body>
</html>
Yes, you can load simple HTML content by using template property as shown in the highlighted code below.
myApp.config(function ($stateProvider, $urlRouterProvider) {
$stateProvider
.state('About', {
url: '/About',
template: '<b>This is About us</b>'
})};
To create a controller, we need to use controller property of the state provider. To specify parameters, you can put the parameter name after the url. In the below code, you can see ‘Id’ parameter after the url and also you can see how validations are applied on these parameters using regex.
myApp.config(function ($stateProvider, $urlRouterProvider) {
$stateProvider
.state('State1', {
url: '/SomeURL/{Id:[0-9]{4,4}}',
template: '<b>asdsd</b>',
controller: function ($scope, $stateParams) {
alert($stateParams.Id);
}
});
First, let us understand the concept of nested views. We want to navigate as follows in SPA. From main view, we want to navigate to some view and in that view, we want to load some other view.
Angular UI Router helps to define nested states. Below is the code of MainView in which we have defined one more state View and in that we have two child states View.SubView1 and View.SubView2 which points to different views.
myApp.config(function ($stateProvider, $urlRouterProvider) {
$stateProvider
.state("View", {
templateUrl: 'View.htm'
})
.state('View.SubView1', {
template: '<b>Sub view 1</b>'
}).state('View.SubView2', {
template: '<b>Sub view 2</b>'
});
});
In the part view, we can now define navigation to child states, i.e., View.SubView1 and View.SubView2.
<a ui-sref="View.SubView1" href="#View.SubView1">Sub view 1</a>
<a ui-sref="View.SubView2" href="#View.SubView1 ">Sub view 2</a>
<div ui-view></div>
Till now, we have looked in to predefined Angular directives like ng-controller, ng-model and so on. But what if we want to create our own custom Angular directive and attach it with HTML elements as shown in the below code.
<div id=footercompany-copy-right></div>
To create a custom directive, we need to use the directive function to register the directive with Angular application. When we call the register method of directive, we need to specify the function which will provide the logic for that directive.
For example, in the below code, we have created a copyright directive and it returns a copyright text.
Please note app is an angular application object which has been explained in the previous sections.
app.directive('companyCopyRight', function ()
{
return
{
template: '@CopyRight questpond.com '
};
});
The above custom directive can be later used in elements as shown in below code.
<div ng-controller="CustomerViewModel">
<div company-copy-right></div>
</div>
For angular custom directive, the best practice is to follow camel casing and that also with at least two letters. In camel case naming convention, we start with a small letter, followed by a capital letter for every word.
Some example of camel cases are loopCounter, isValid and so on.
So when you register a custom directive, it should be with camel case format as shown in the below code companyCopyRight.
app.directive('companyCopyRight', function ()
{
return
{
template: '@CopyRight questpond.com '
};
});
Later when this directive is consumed inside HTML before each capital letter of camel case, we need to insert a - as specified in the below code.
<div company-copy-right></div>
If you are making a one letter prefix like copyright, it’s very much possible that tomorrow if HTML team creates a tag with the same name, it will clash with your custom directive. That’s why Angular team recommends camel case which inserts a - in between to avoid further collision with future HTML tags.
There are different flavors of Angular directives depending till what level you want to restrict your custom directive.
In other words, do you want your custom directive to be applied only on HTML element or only on an attribute or just to CSS, etc.
So in all, there are four different kinds of custom directives:
- Element directives (E)
- Attribute directives (A)
- CSS class directives (C)
- Comment directives (M)
Below is a simple custom directive implementation at the element level.
myapp.directive('userinfo', function()
{
var directive = {};
directive.restrict = 'E';
directive.template = "User : {{user.firstName}} {{user.lastName}}";
return directie;
});
The restrict property is set to E which means that this directive can only be used at element level as shown in the code snippet below.
<userinfo></userinfo>
If you try to use it at an attribute level as shown in the below code, it will not work.
<div userinfo></div>
So E for element, A for attribute, C for CSS and M for comments.
directive.restrict = 'EA';
Yes, you can set template to page directly by using templateUrl property of the directive as shown in the code snippet below.
directive.templateUrl = "/templates/footer.html";
Promises are POST PROCESSING LOGICS which you want to execute after some operation / action is completed. While deferred helps to control how and when those promise logics will execute.
We can think about promises as WHAT we want to fire after an operation is completed while deferred controls WHEN and HOW those promises will execute.
For example, after an operation is complete, you want to a send a mail, log in to log file and so on. So these operations you will define using promise. And these promise logics will be controlled by deferred.
We are thankful to www.stepbystepschools.net for the above image.
So once some action completes, deferred gives a signal Resolve, Reject or Notify and depending on what kind of signal is sent, the appropriate promise logic chain fires.
$q is the angular service which provides promises and deferred functionality.
Using promises, deferred and q service is a 4 step process:
- Step 1: Get the
q service injected from Angular. - Step 2: Get deferred object from
q service object. - Step 3: Get
Promise object from deferred object. - Step 4: Add logics to the promise object.
Below is the Angular code for the above four steps.
function SomeClass($scope,$q) {
var defer = $q.defer();
var promise = defer.promise;
promise.then(function () {
alert("Logic1 success");
}, function () {
alert("Logic 1 failure");
});
promise.then(function () {
alert("Logic 2 success");
}, function () {
alert("Logic 2 failure");
});
}
So now depending on situations, you can signal your promise logics via deferred to either fire the success events or the failure events.
defer.resolve();
defer.reject();
For further reading, do watch the below interview preparation videos and step by step video series.
