AngularJS Interview Questions Answers
AngularJS Interview Questions
- It allows you to use HTML as your template language and enables you to extend HTML's syntax to express your application's components clearly
Initially, it was developed by Misko Hevery and Adam Abrons. Currently, it is being maintained by Google.
- Supports two way data-binding
- Supports MVC pattern
- Support static template and angular template
- Can add custom directive
- Supports REST full services
- Supports form validations
- Applying Animations
- Event Handlers
- AngularJS code is unit testable.
- AngularJS provides reusable components.
- Support both client and server communication
- AngularJS, developer write less code and get more functionality.
- AngularJS uses dependency injection and make use of separation of concerns.
- AngularJS provides the capability to create Single Page Application in a very clean and maintainable way.
AngularJS applications can run on all major browsers and smartphones including Android and iOS-based phones/tablets.
- Data Binding
- Model View Controller
Automatic synchronization of data between the model and view components is referred as data binding in AngularJS.
There are two ways for data binding
- Data mining in classical template systems
- Data binding in angular templates
- To observer model mutations scopes provide APIs ($watch)
- To propagate any model changes through the system into the view from outside of the Angular realm
- A scope inherits properties from its parent scope, while providing access to shared model properties, scopes can be nested to isolate application components
- Scope provides context against which expressions are evaluated
Some of the commonly used directives are:
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AngularJS Interview Questions
- No Control Flow Statements: Loops, conditionals or exceptions cannot be used in an angular expression
- Filters: To format data before displaying it you can use filters
- <div ng-controller = "apps/dashboard/account" ng-switch
- On = "!! accounts" ng-init = "loadData()">
- Registering Callbacks: There is no need to register callbacks . This makes your code simple and easy to debug.
- Control HTML DOM programmatically: All the application that are created using Angular never have to manipulate the DOM although it can be done if it is required
- Transfer data to and from the UI: AngularJS helps to eliminate almost all of the boiler plate like validating the form, displaying validation errors, returning to an internal model and so on which occurs due to flow of marshalling data
- No initilization code: With AngularJS you can bootstrap your app easily using services, which auto-injected into your application in Guice like dependency injection style
In Angular.js the compiler during the compilation process matches text and attributes using interpolate service to see if they contain embedded expressions. As part of normal digest cycle, these expressions are updated and registered as watches.
Compilation of HTML process occurs in following ways
- Using the standard browser API, first the HTML is parsed into DOM
- By using the call to the $compile () method, compilation of the DOM is performed. The method traverses the DOM and matches the directives.
- Link the template with scope by calling the linking function returned from the previous step
Link combines the directives with a scope and produces a live view.
For registering DOM listeners as well as updating the DOM, link function is responsible. After the template is cloned it is executed.
- Pre-linking function: Pre-linking function is executed before the child elements are linked. It is not considered as the safe way for DOM transformation.
- Post linking function: Post linking function is executed after the child elements are linked. It is safe to do DOM transformation by post-linking function
An injector is a service locator. It is used to retrieve object instances as defined by the provider, instantiate types, invoke methods and load modules.
There is a single injector per Angular application, it helps to look up an object instance by its name.
- Compile function: It is used for template DOM Manipulation and collect all of the directives.
- Link function: It is used for registering DOM listeners as well as instance DOM manipulation. It is executed once the template has been cloned.
For creating the directive, the factory method is used. It is invoked only once when compiler matches the directive for the first time. By using the $injector. invoke the factory method is invoked.
ngModel adds these CSS classes to allow styling of form as well as control
- ng- valid
- ng- invalid
DI or Dependency Injection is a software design pattern that deals with how code gets hold of its dependencies. In order to retrieve elements of the application which is required to be configured when a module gets loaded, the operation "config" uses dependency injection.
These are the ways that object uses to hold of its dependencies
- Typically using the new operator, dependency can be created
- By referring to a global variable, dependency can be looked up
- Dependency can be passed into where it is required
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Each angular application consists of one root scope but may have several child scopes. As child controllers and some directives create new child scopes, an application can have multiple scopes. When new scopes are formed or created they are added as children of their parent scope. Similar to DOM, they also create a hierarchical structure.
- Angular has integrated built-in utilities, which help to validate client input before it gets processed or sent to a server;
- Angular has dedicated debugging tools;
- Angular checks for any changes and updates the corresponding fields;
- Angular has a popular plugin which includes facilities to create view animations.
- Backbone allows to integrate third party libraries well;
- Backbone uses observables for data binding (it observes Models);
- Backbone has a possibility to be extended in order to support models and views updating each other;
- Backbone might work well with other template engines (more than one).