Introduction
Despite the transition towards more advanced frameworks in modern times, traditional enterprise applications around the world continue to depend greatly on AngularJS (Angular 1.x). To successfully pass an interview about AngularJS, one needs to be well familiar with the specific architectural structure, digest loops, and two-way data binding in AngularJS.
The following list includes important AngularJS interview questions and answers, presented in a systematic way, starting from the main directives and ending with scope management.
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AngularJS Interview Questions and Answers for Freshers
1. What is AngularJS?
AngularJS is an open-source, structure-based JavaScript framework developed by Google. It adds custom attributes to HTML using directives and implements an MVC framework on the client-side to make web application development easier.
2. What is the difference between AngularJS and Angular?
AngularJS is the first version 1.x based on JavaScript with a controller-driven architecture. Angular is the newer version 2+ that is fully rewritten as a component-based framework completely in TypeScript.
3. What are directives in AngularJS?
The directives are special markers that can be placed either in the attributes, element names, or CSS classes of DOM elements, telling AngularJS what specific behavior to apply to it or to transform this DOM element into an interactive component.
4. Describe some of the most common built-in AngularJS directives.
Among the most common directives are ng-app (starts an AngularJS application), ng-model (binds the value of HTML controls to application data), ng-bind (substitutes the content of HTML with data values), and ng-repeat (iterates through a collection).
5. What is data binding in AngularJS?
Data binding is the synchronization process of data automatically between the model and the view. In AngularJS, two-way data binding is used where changes to the model reflect instantly in the view and changes in the view reflect in the model immediately.
6. Explain the $scope object in AngularJS.
The $scope is a JavaScript object that is used as a bridge between the application controller and the HTML view. The $scope contains all the data that we want to make available to our UI templates as well as some functions.
7. Explain the $rootScope in AngularJS.
$rootScope is the root-level parent scope created in the HTML element that is decorated with the ng-app attribute. All other scopes are child scopes of the $rootScope, and hence its properties are available to the entire application.
8. Explain the MVC architecture in AngularJS.
In AngularJS MVC architecture, the model represents the database or JSON data in the scope. View is the HTML template that displays the model, and the controller manages the business logic for managing data flow.
9. What are expressions in AngularJS?
Expressions are JavaScript-like code snippets written inside double braces {{ expression }}. They are evaluated by AngularJS, and the resulting string value is directly output and rendered inline within the HTML view.
10. What is a controller in AngularJS?
A controller is a JavaScript constructor function defined by the ng-controller directive. It is primarily used to set up the initial state of the $scope object and add behavior or functions to it.
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11. What are filters in AngularJS?
Filters are functions that help to manipulate or format data before rendering it in the view. Filters can be used in both templates and controllers to accomplish tasks such as formatting currency, dates, and filtering arrays.
12. What is Dependency Injection (DI) in AngularJS?
Dependency Injection is an inherent design pattern that passes components to their dependencies rather than building their dependencies. The AngularJS framework utilizes DI by injecting services like $http and $location into controllers.
13. Purpose of the $http service.
$http is a vital service in the AngularJS framework, which enables you to communicate asynchronously with your HTTP server. It makes use of the XMLHttpRequest object in the browser to make requests for data.
14. What is the difference between a Factory and a Service?
Factory is a function that executes one time and returns an initialized JavaScript object with methods. Service is a constructor function that is created using the ‘new’ keyword, and its methods are exposed using the ‘this’ keyword.
15. What are validation features in AngularJS forms?
AngularJS provides client-side form validation by tracking form states automatically. It provides boolean properties like $valid, $invalid, $dirty, and $pristine on input fields to dynamically show error messages based on validation states.
AngularJS Interview Questions and Answers for Experienced Candidates
1. Describe the architectural process involved in the AngularJS Digest Loop. What is the interaction between $watch, $digest, and $apply?
AngularJS uses the digest loop for dirty checking. Asynchronous operations that occur out of the AngularJS context are invoked by using $apply(), which initiates a $digest() loop starting at $rootScope.
The loop will go through all of the $watch expressions and check whether there are changes relative to the old value. The loop keeps going until the data becomes stable (10 iterations TTL).
2. How will you identify and tune an underperforming AngularJS application that is facing serious digest cycle latency?
The reason for latency is usually high data binding. There are some ways to tune your app:
- Use one-time binding: Apply double colon syntax ({{::user.name}}), which will unbind an element when it’s resolved and will remove it from the watch list.
- Use track by in ng-repeat: Reuse your DOM nodes rather than rebuilding them when the array changes.
- Use debouncing on input: Apply ng-model-options=”{ debounce: 300 }”.
3. Describe the distinction between the compilation and linking operations in a custom AngularJS directive.
The directives handle UI updates using a different two-step process:
angular.module(‘app’).directive(‘myDirective’, function() {
return {
// Step 1: Transforms the template DOM once across all instances. No scope is available here.
compile: function(tElement, tAttrs) {
return {
// Step 2: Binds data scope to the cloned DOM instance. Safe for DOM manipulation.
pre: function(scope, iElement, iAttrs) {},
post: function(scope, iElement, iAttrs) {
iElement.on(‘click’, function() {});
}
};
}
};
});
4. Compare the scope binding configuration options and considerations for (@, =, &).
Isolated scopes ensure that the directives do not inadvertently change the parent controller data.
| Symbol | Binding Type | Mechanism | Use Case |
| @ | Text/String Binding | One-way evaluation of HTML attribute strings. | Passing plain configuration strings or fixed values. |
| = | Two-way Binding | Creates a live bi-directional link between parent and child. | Syncing form components or active data models. |
| & | Expression/Callback | Evaluates wrapper functions within the parent context. | Invoking event handlers or streaming data upward. |
5. What would be the technique for implementing a good nested tab layout component using Directive-to-Directive communication through “require”?
To set up a good child-to-parent communication structure, one can use the “require” attribute. It will allow injecting a nested child directive into the parent’s controller API.
// Child directive
angular.module(‘app’).directive(‘myTabPane’, function() {
return {
require: ‘^myTabContainer’, // Injects the parent controller instance
link: function(scope, element, attrs, containerCtrl) {
containerCtrl.addPane(scope); // Call parent API directly
}
};
});
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6. Describe the behavioral distinction between “scope: true” and “scope: {}” in an AngularJS directive.
- Setting Scope: true makes AngularJS create a child scope with prototypal inheritance from its parent scope. It allows reading of parent variables and writes primitives to override them in the child scope.
- Setting Scope: {} results in an isolated scope without inheriting any of its parent scope properties. This makes the directive independent of its environment and re-usable as a widget.
7. What are the steps to create a scalable HTTP interceptor that will refresh OAuth tokens that have expired?
One way to implement this is to add the interceptor service within the config block of your application by using the $httpProvider:
angular.module(‘app’).factory(‘authInterceptor’, function($q, $injector) {
return {
responseError: function(rejection) {
if (rejection.status === 401) {
// Use $injector to avoid circular dependency errors
return $injector.get(‘authService’).refreshToken()
.then(() => $injector.get(‘$http’)(rejection.config));
}
return $q.reject(rejection);
}
};
});
8. Compare the design patterns and lifecycles of Service, Factory, and Provider.
All three architecture design patterns are singletons, but they provide different degrees of initialization flexibility:
- Factory: This is a function that executes only once and produces a customized object. Very versatile for designing generic utilities.
- Service: This is a constructor function instantiated by the new keyword and exposes methods using ‘this’.
- Provider: The most configurable of all. It provides a $get method and allows module-level configuration using .config() sections before application execution.
9. Discuss how the $q service works with promises and deals with complex dependencies using $q.all().
The $q service allows the resolution of code asynchronously. In case you want to make multiple HTTP requests simultaneously and want to perform some business logic after they finish, use $q.all().
var profilePromise = $http.get(‘/user/profile’);
var settingsPromise = $http.get(‘/user/settings’);
$q.all([profilePromise, settingsPromise]).then(function(responses) {
$scope.profile = responses[0].data;
$scope.settings = responses[1].data;
});
10. How can you make a dynamic UI routing state machine by using ui-router with data pre-loading using resolve?
Using the ui-router module, you can achieve advanced state management capabilities. To do this, you need to define a resolve method that ensures all the data is retrieved before displaying any view:
$stateProvider.state(‘dashboard’, {
url: ‘/dashboard’,
templateUrl: ‘dashboard.html’,
resolve: {
initialData: function(apiService) {
return apiService.getDashboardSummary(); // Prevents blank views
}
}
});
11. What is the advantage of using the controllerAs syntax versus traditional $scope object injection in production applications?
This controllerAs syntax treats the controllers as traditional JavaScript classes and binds the model variables to this, rather than injecting $scope into controllers. In complicated user interfaces where there are many nested views, controllerAs syntax removes all problems with prototypical inheritance of scopes. ControllerAs syntax requires explicit namespace usage in HTML templates (vm.title) that makes code much cleaner.
12. How do you achieve global state management or intercontroller communication without resorting to $rootScope.$broadcast?
The problem with $rootScope.$broadcast is that it will affect the performance since the event is propagated down to all active children scopes and triggers the dirty check.
To solve the issue, create a centralized Singleton Service acting as the state machine and let the controllers inject it to bind to the shared data references. For reactive updates use either RxJS-like subject observables or simple function callbacks inside the service.
13. What precautions do you need to follow to protect your AngularJS-based web application from XSS attacks?
In the case of AngularJS, there is a built-in security system known as strict contextual escaping ($sce), which, by default, would not render HTML using ng-bind-html if any unsafe script pieces exist in the string.
If you want to handle rich text, make sure that you have the ngSanitize module included; this module removes any malicious HTML from the text inputs and keeps the safe formatting tags untouched.
14. What do you need to consider to migrate your existing AngularJS-based application into modern Angular (v2+ )?
This is done through the use of the @angular/upgrade module, which enables running both frameworks at once within the same browser-based application shell.
It is possible to bootstrap your existing application inside a new Angular application container and, thus, migrate its components incrementally:
// Example of a modern component downgrading to work inside AngularJS
import { downgradeComponent } from ‘@angular/upgrade/static’;
angular.module(‘legacyApp’).directive(‘modernChart’, downgradeComponent({ component: ModernChartComponent }));
15. What is the best way to do memory management and avoid memory leaks within custom directives where global events are registered?
The reason for memory leaks arises when listeners are attached to global objects like window, document, or $rootScope but are not detached upon removal of the directive from the DOM.
The way to avoid them is to always listen to the scope destruction event and remove the listeners yourself.
scope.$on(‘$destroy’, function() {
$document.off(‘keydown’, globalKeydownHandler); // Cleans up reference links
});
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Conclusion
Going through an AngularJS technology interview demands knowledge about old front-end architecture, component life cycle, and advanced performance tuning, such as control over the digest loop. The ability to maintain, secure, and migrate legacy front-end systems is going to make you an invaluable member of teams doing large web projects.
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