Angular 4 Interview Questions

An Overview of Angular 4

Angular 4, released in March 2017, is a JavaScript framework for building apps in HTML, JavaScript, and TypeScript. Angular 4 offers built-in features for HTTP service, animation, and materials. This is an essential topic in Angular 4 Interview Questions for experienced professionals.

The unique feature in Angular 4 is that starting from Angular 4, developers will be able to query ParamMap in the router. This means a request for the route- and query parameter can be assigned to a route. Until Angular 2, route parameters were stored in a key-value object and were accessible through standard JavaScript syntax.

Another unique feature is that the functions that were necessary for animations are placed in their package. This has been done to avoid creating unnecessary bundles of significant size. Until Angular 2, these functions were offered as part of the core module and were always included even if they were not getting used in apps.

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In angular 4, the use of decorators is done extensively for compiling the code. There are four types of decorators – Class, Property, Method, and Parameter.

Type security and speed of ngc-Compiler have improved in Angular 4 as compared to Angular 2.

You can also find here Angularjs Interview Questions , Angular 4 Interview Questions , Angular 6 Interview Questions

Angular 4 Interview Questions and answers

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Angular 4 is an advanced JavaScript framework which uses HTML, JavaScript, and TypeScript web applications and APK apps. It’s a superset of JavaScript and offers excellent built-in features for HTTP service, animation, navigation, menus, toolbar, materials, etc.

Angular 4 has several new feature additions. As most of the changes are implemented to the background rather than its core functionality of coding, it’s being called an invisible makeover to its previous version. The compiler error messages have improved as well as the code generation. According to the Angular team, patches will be released every week. All the major releases will be followed with minor Angular release. In every six months, there will be a significant release for the framework which will be easy to integrate breaking changes. It also has the potential to improve performance when used appropriately. The structure now also supports TypeScript 2.1+.

Angular 4 was released with many great features and excellent improvements compared to its previous version.

Here are a few of them mentioned below:
  • Smaller and faster
  • 60% less code in view engine
  • Separate animation package
  • A new else statement for nglf.
  • Angular apps now can be rendered on the servers using Angular Universal.

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Here are a few significant differences between Angular 2 and 4 which developers are going to notice.
  • Angular 4 has many inbuilt animation packages which were missing in Angular 2.
  • Angular 4 has its template tag called “ng-template.” The previous version uses only “template.”
  • Compared to Angular 2, in the newest version, developers can use else syntax with Nglf for excellent UI handling.
  • A new template syntax addition “as keyword” in Angular 4 which can be used to simplify to the “let” syntax.
  • Simplified “HTTP request” and application testing in Angular 4.

AngularJS is the very first version of the Angular. A tool named AngularCLI is used to generate Angular components. Angular JS which is a client-side framework works with JavaScript and still supported but not compatible with Angular any more. Simplifying it, AngularJS is the old version and Angular is the newest one.

To set Http Request Header in Angular 2, create the HTTP Client Injectable class and inject the HttpClient object in the Component. Developers use HTTP Interceptors to set Http Request Header in Angular 4. To achieve this. Write an interceptor for adds a header for every request and after creating the interceptor, register it using HTTP_INTERCEPTORS in the @NgModule().

There are two types of errors in Angular 4.
  • Background returns an unsuccessful response such as 500, 404 and so on.
  • Client-side errors such as network error, etc.

In both cases, we use HttpErrorResponse and return the crucial information on what went wrong with the call.

To create a new component in Angular 4 using CLI,
  • Open Project Directory
  • Run any one of the below mentioned the syntax

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ng component name


ng generate component componentname

No coding level changes are required to enhance a project present in Angular 2 to Angular 4. Users only have to update the tsconfig.json and package.json files. Some minor adjustments may be needed depending on project types. After updating the data, clean out your node_modules directory, run npm install and npm start and you will be started with the Angular 4.

In Angular 4, the ForRoot method is used when the module is "eager," not lazy-loaded. Except for lazy modules which loaded on demand with their factory, Angular creates a factory for all other modules. The ForRoot method allows users to access providers from any point in the application that is not lazy loaded. This ultimately will enable users to have different configurations for different load cases.

Angular 5 has plenty of new features. Few of the most important ones are mentioned below:
  • Addition of a build optimizer which removes unnecessary applications and codes.
  • Support for DOM and Angular Universal State Transfer API.
  • Optimized standardization across various browsers.
  • Addition of a new HttpClient and lifecycle events router.
  • Creation of Angular 5 projects by default with CLI 1.5.
  • Multiple name support for directives and components.

Compared to Angular 4, Angular 5 has plenty of feature additions, bug fixes and service improvements implemented to it. The addition of a build optimizer to Angular 5 is a pleasant surprise for developers. Added to CLI, this tool can help developers to create smaller bundles for the application. It also increases the boot speed of the application for users. Few other crucial differences between these two versions will be compiler improvements, the addition of HttpClient and new router lifecycle events. All these features have newly included to the Angular 5.

There are various ways available to install Angular 4.
  • Install the Angular CLI
    npm install -g @angular/cli
  • Create a Project
    ng new MyApp
  • Serve the application
    cd MyApp
    ng serve --open

This information can be asked during angular 4 interview questions.

In Angular 4, components have their view, whereas directives are just “behavior” added to the existing components and elements. Simplifying it, components extend directives. There can be many directives on a host element, but only one component.

Unit testing or private testing is used to test the system’s components. This process is s best practice to test small separate pieces of code. If the unit testing depends on any of the external resources such as networks, APIs and databases, then it won’t be listed as a unit test.

In Angular 4, template reference variables allow users to access an instance of a directive or component or a DOM present in the template. These are defined by a hash sign (#) combined with a name as an additional DOM element’s attribute.

In Angular 4, data binding is a core concept that allows defining communication between the DOM and a component. This makes it easy to define interactive applications without complexion of pulling and pushing data.

In Angular 4, there are four types of component decorators:
  • Class decorators
  • Property decorators – used for properties inside classes
  • Method decorators – used for methods inside classes
  • Parameter decorators – used for parameters inside class constructors

This information is usually asked in interview questions on Angular 4.

In AngularJS, JSON Web Token is used to send information which can be trusted and verified using a digital signature. The JSON Web Token comprises a URL-safe and compact JSON object, which is cryptographically signed to verify its authenticity. This also can be encrypted if the payload contains any sensitive information.

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