Angular 6 Interview Questions & Answers (2025)

The BehaviorSubject is used to hold the values that are to be shared with other components. You can subscribe to data with the BehaviorSubject that needs to be shared with other components.

You can subscribe to the data using the Behavior Subject service as the following.

//inject service into a component
dataService.data.subscribe(data => {
  //do whatever needs doing when data changes
})
//update the value of data in the service
dataService.updateData(newData);

The fork-join operator is used when you need to wait for multiple HTTP requests to be resolved. It groups all the observables returned by each HTTP call into a single observable array. Finally, it returns the observable array.

Codelyzer is a tool used for static analysis of the Angular TypeScript projects. This tool sits on the top of TSLint and checks if the Angular TypeScript projects follow the set of linting rules. It has over 50 rules to check the Angular projects. You can add this tool using the npm package manager to your project. This tool can be used to run the static code analyzer over web apps, native script, ionic, etc.

Latest Key features of Angular 6

• Added support for creating Custom Elements based on Angular Components.
• Animations: expose element and params within transition matchers.
• Bazel: change ng_package rule to APF v6
• singleline, multiline and jsdoc comments are now supported
• compiler-cli : add resource inlining to ngc
• support for TypeScript 2.7
• Require node 8 as runtime engine

Ivy Renderer is the next generation renderer to serve the purpose of enhanced performance. The Ivy renderer decreases the bundle size and the loading time which improves the performance and moreover, it streamlines the usage as well. The Ivy renderer is simple to use and easy to debug. This new pipeline skips angular interpreter and template data structures. These bundles can be further optimized with the help of Code splitting.

Bazel is a built tool introduced with the Angular 6 that is used extensively by Google. It is mainly used to optimize the angular compilation and improves the building and test on Angular apps.

The Closure in Angular JS is the combination of a function that is enclosed with references to its surrounding state. It gives you access to the outer scope of the function from an inner function. Closures are created in JavaScript every time a function is created at the creation time.

Service Worker is a script that runs in the web browser to manage the message caching for an application. It empowers the application to deliver user experience with reliability and performance that is on par with the natively-installed applications. It is one of the steps that turn an application into Progressive Web Applications. It also works as a network proxy. It intercepts all the outgoing HTTP requests by the application and chooses how to respond to them.

You can generate a component in specific module in AngularJs by running below commnad on CLI.

ng g component component_name --module=module_name

In order to generate a module in Angular, cd to the current project directory and below command.

ng g module module_name

Zones are a kind of performance setting that empowers us to catch into our anachronistic tasks.

Zones in angular APIs increase the performance by executing our code exterior to the angular zone. It helps in preventing Angular from the governing unwanted alter detection assignments.

In order to upgrade angular-cli package that was installed globally in your system, you need to run following commands

npm uninstall -g angular-cli
npm cache clean or npm cache verify (if npm > 5)
npm install -g @angular/cli@latest

Instead of upgrading global version of angular-cli you can also upgrade the local version for specific project y running following commands:

rm -rf node_modules
npm uninstall --save-dev angular-cli
npm install --save-dev @angular/cli@latest
npm install

Below are the list of few Pipes available in Angular Js

• DatePipe
• CurrencyPipe
• AsyncPipe
• DecimalPipe
• TitleCasePipe
• JsonPipe
• SlicePipe
• PercentPipe
• UpperCasePipe
• LowerCasePipe

The observable in Angular 6 can be implemented using the RxJS library to work with the asynchronous events. The RxJS gives a number of functions to create new observable to simply the process of creating it from things such as events, timers, promises, and so on.

You can create an observable from a promise, a counter, an event, from an AJAX request.

An observable is implemented using the RxJS library to work with the asynchronous events and it provides a way of publishing data in JavaScript. You have to subscribe to the observable to receive values from the observables. To subscribe to the observable, you can use either async pipe or using the actual subscribe method. You can perform operators such as map(), filter(), Concat(), and flatMap() with the observable.

Cancel and unsubscribing Observable are the same thing. You can use the unsubscribe function over the subscription object to unsubscribe the observable in Angular 6. You can also use the async pipe or the takeUnitil operator in Angular 6 to can cancel the observable.

You should subscribe to your observable to convert into an array.

There are six ways to unsubscribe from the observable in Angular 6.

• You can use the actual unsubscribe method to cancel observable executions.
• You can use the Async | pipe to unsubscribe automatically as the component gets destroyed.
• The take* operators in the RxJS can be used to unsubscribe if it is called with no value.
• The Decorator can be used to automate unsubscription.
• The RxJS first operator is used to cancel an observable.
• The tslint can be used to remind the console that the components or directive should have a ngOnDestroy method when it detects none.

Linting is the process of running a program that analyses your code for programmatic and stylistic errors. It checks the code quality of the angular project specified.

The @HostListener is a decorator method in Angular 6 that is used for listening to DOM events. It listens to the DOM events on the host element of both the component and attribute components. It sets the listener once when the directive is initialized and removes the listener if the directive is destroyed.

The system.config.json file is used to configure the SystemJS for the Angular application. It also allows for different modules to load compiled using the TypeScript compiler.