30+ Angular 2 Interview Questions To Hire Or Get Hired With

Angular 2 is an important staple in the toolkit of any developer. As web apps are becoming more like native applications with the serving of content in real-time on the front-end of the server, Angular 2 has become a useful part of the polyglots workflow. The advantage of this javascript-based framework is that it allows for advanced engineering to take place on the front-end, theoretically replacing the need for expensive requests to the backend. This provides the end user with an amazing experience and even allows them to have offline modes of interaction with the product or service. This can be especially advantageous for those building mobile applications where signal strength can often be weak. Most commonly, similar types of applications of this methodology, including other front-end frameworks, in tools like Gmail. When a user writes an email, it is consistently autosaved. This javascript function provides advantages for the user that reduce significant friction. These Angular 2 interview questions and answers should provide you with an effective study guide to prepare you for your next interview. As with all Q&A's, it is recommended that you find a way to answer these questions using your own speaking mannerisms and personal methods of delivery. Practicing with a friend or family member is always a great idea.

1. Can you tell me what is angular 2 is?

Angular 2 refers to a revised element-based JavaScript framework where an application is a tree of loosely-coupled components. It is significantly more advanced than Angular JS and is effectively a comprehensive all-in-one overall framework. Therefore, it also assists in increasing the size and efficiency of a single website without being trapped into different JS frameworks. Angular 2 is modular as a framework, meaning that the code is divided into individual procedures, which give a similar functionality in order to improve the testing, gradation and the maintenance of the platform. There are several useful attributes of the angular system, including the server-side rendering, cross-platform, and the support of multiple languages, something many predecessors cannot claim access to. It is a new typescript framework that is constructed from the concept of those elements which allow for better development. Hybrid applications using this framework are also given a sharp edge over the competition by providing the flexibility of similar standard codes for the development of platforms.

2. What are the core programming elements within Angular 2?

• Modules are utilized for breaking the application into logical pieces of code. Each of the pieces are then designed specifically to perform a single task.
• Templates are used to define the aesthetic views of the application.
• Metadata is employed in order to add additional data to the Angular JS class.
• Components are used to bring these modules together.
• Services are utilized to create components that can be shared across the application.

3. What are the components inside of Angular 2?

Each application has components and each component is a logical boundary that provides functionality to the application. One needs to have layered services that are used for sharing the functionality across the different components. A component entails the following:

• Class is like a Java class or C, which has its own properties and methods.
• Metadata is utilized to decorate the class and extend the functionality of the class.
• Template is used to define the HTML perspective that is displayed within the application.

4. Can you tell me what modules are in Angular 2?

The modules are used to place logical boundaries in the application. As such, as opposed to coding everything into one application, users can instead code everything into separate modules for the purpose of splitting the functionality of the application. The Module entails the following parts:

• Bootstrap array; this can be used to tell the framework which components need to be loaded so that the functionality can be accessed within the application. At the point at which the component within the bootstrap has been included, users need to declare them so they can be used across the other components within the framework.
• Import array; the import array can be used to import functionality from the other modules.
• Export array; this is used for the exportation of directives, components, and popes that can be utilized within many other modules.

5. What are some of the newer features within Angular 2?

Angular 2 is written completely in typescript and meets the ECMAScript 6 particulars. This primarily means that:

• It is component based; the $scope and controllers are no longer relevant. They have been replaced by directives and components.
• Directives; directive specifications are still very simplified, though they are subject to significant change. With the @Directive annotation, a directive may be declared.
• The use of typescript; typescript is a typed super-set of the JavaScript language which has been created and maintained by Microsoft for this specific project. The presence of types makes the code written less prone to run-time issues. During more recent updates, the support for ES6 has been improved significantly and a number of features from ES7 have been added as well.
• Lambdas with TypeScript; in TypeScript, lambdas are available.
• Dependency injection; because of the improvement dependency injection model within Angular 2, there are more chances for the component or object-based work.
• Generics: TypeScript has a number of generics which can be utilized in frontend operations..
• Forms and validation: these are some of the most significant elements of frontend development. In Angular 2, the Form Builder and Control Group are defined.

6. What are some of the benefits of Angular 2?

Angular 2 is not just the usual upgrade, but represents a complete overhaul of the previous platform. The entire framework was rewritten from scratch. Angular 2 got rid of components including controllers, $scope, DDO, jqLite, Angular.module and many more. The components are used for practically everything. Imagine that the entire application is currently one big component. It also benefits from ES6 or TypeScript syntax. The development of Angular 2 apps in TypeScript has made it even stronger; several things have evolved and been re-designed.

7. What is TypeScript?

TypeScript refers to a typed superset of JavaScript that has been initiated and maintained by Microsoft. It has also been chosen by the Angular framework for development.

8. What is ECMAScript?

ECMAScript is a subset of JavaScript. JavaScript is ECMAScript at the core, but develops and builds upon it significantly. Languages like ActionScript, JavaScript and Jscript all utilize ECMAScript at their core. As a comparison, think of AS, JS, and Jscript as three different motor vehicles which all use the same engine. Each of their exteriors are different and they have been each modified to uniqueness. In this case, Angular 2 utilizes ES6 and higher versions.

9. What is @ngmodule?

NgModule refers to a decorator function. These functions provide a chance for users to mark something like Angular 2, and it allows them to provide additional data to determine how the “Angular 2” is going to be processed, instantiated, and utilized during the runtime. This means that now whenever the user writes @NgModule, it communicates to the Angular 2 module what is going to be included and utilized within the module.

10. Can you tell me what the Traceur Compiler is?

Traceur refers to a JavaScript.next-to-JavaScript-of-today compiler, which allows an individual to use the features from the future at the present. Traceur supports ES6 as an experimental ES.next features. The goal of the Traceur is to inform the design of the new JavaScript type features that would be only valuable in they allow one to write a better code.

11. What are @inputs in the context of Angular 2?

@input allows one to pass data into the controller and templates through the html and defining custom properties. This would allow a user to reuse the components and then have them illustrate the different values for each scenario of the renderer.

12. How does an engineer define a transition between two states in angular?

The transitions made between two states take place in a way that makes it possible to build animations between the two states driven by a model attribute. The concept of transition means the navigation from one state to another. In Angular, the transition is an animation-specific type of function that is used within the framework’s animation DSL language. Transition declares the sequence of the animation steps, which are then implemented when the entered value is satisfied. A function is then given an argument for a transition and it is implemented each time this specific state change happens. In this way, if the function is correct, the animation is either going to run or will not be implemented at all. These animation transitions are then situated within the animation triggers. The transition may be dependent on what the animation was in the previous state, or on what it is going to be in the next state. That would mean that if a transition is defined according to a way that matches the old or present state criteria, then the associated animation is going to be triggered.

13. How do you declare a component in Angular 2?

Components in Angular 2 are just directives, which are linked with one another via a direct template. Angular 2 components have a very well-defined life cycle. When working with angular components, it becomes possible to make use of interfaces, which can implement functionality at different times in the life cycle of a component. The component must belong to an NgModule for it to be utilized by another application or component. The components might even control their runtime behavior through the implementation of different lifecycle hooks. Components always have a template and only one of the components may be instantiated for every element within a template. When the component has been initiated, Angular then creates a change detector that propagates the construction of the component.

14. What is the difference between promises and observables?

• An observable is a stream that allows passing zero or more events in which callback occurs in each event. Alternatively, a promise eventually calls the success or failed callback, even when notification of result is not given..
• Observable is a significant way to handle the HTTP asynchronous requests. But remember, a promise just handles a single event when an asynchronous operation either fails or completes.
• Observable works with a number of values for a set time, while promises work with and even return a single value at any given time.
• Observables support the map, as well as filter and reduce similar operators. The promises happen often have more readable codes with async/await and try/catch.
• Promises cannot be canceled, but observables can be.
• When it comes to observables, an operator ‘retry’ may be utilized to retry when needed. On the other hand, promises cannot be retried. A promise should have access to the original function that returned the promise to maintain effective retry capability.

15. What are the differences between directives and Angular 2 components?

Much like components, directives are also utilized in Angular 2, and that allows for the attachment of behavior to the elements in DOM. There are key differences between the components and directives within Angular 2. These typically include:

• In Angular 2, the component is a directive with a view, while a directive is a decorator that does not have a view. Components are a particular type of directive which allows for the utilization of web component functionality throughout the application. Directive refers to the mechanism through which behavior is applied to the elements.
• A component can be used to break the application into smaller parts. The directive is instead used to design the reusable components of the application.
• Components can also be used to help to define pipes. However, it is not possible to define pipes with the use of directives.
• Components can be present for every DOM element, while directives, on the other hand, are used for adding behavior to existing DOM elements.

16. When is the optimal time to use constructor and NgOnInit in Angular 2?

Constructors are utilized for the initialization of class members, as well as for dependency injection. NgOnInit is utilized for the initialization only. Both of these functions are called at the time the component is created. It is important to remember how and when they are used. They are utilized for providing the best structure for the code of the component. The constructor method is one of the pre-defined means in the constructor class called when the class has been instantiated. It may also be used for the proper initialization of the fields. The constructor then in Angular 2 may be used for creating a new instance in the class. NgOnInit is the class that is imported when constructors are implemented for use within a class. The approach that is used in this case is ngOnInit(). This approach assists in the initialization of the directive of the component after the data bound set of properties is illustrated and the directive or the input of the components has been set.

17. Explain the definition and function of a shared module in Angular 2?

The shared module is used for importing the services in both the lazy loaded and eager modules. It is apparent that the lazy-loaded type modules create their branch on the dependency injection tree. The shared module consists of services registered by the angular in the root app injector. There is no need to import this within the lazy module, considering that the lazy-loaded modules already had access to the services as defined at the root. The pipes, directives, and components are also defined within the shared module. The other modules, which import the shared module, would be able to utilize it in their templates. This would mean that the modules would be imported normally in the lazy-loaded module. The shared type module has the code, which will then be used across the applications and the modules as featured. It also entails the common template components. The ‘Dumb components’ also need to be present within the shared module. This usually entails some of the more common angular modules as well. When one is importing the shared module, there will be significant need to import the module with its providers as there is no app module within the test.

18. What is the concept of lazy loading when it comes to Angular 2?

Lazy loading refers to a module that is utilized specifically with the intention of decreasing the startup time. When the lazy module is utilized, the system application does not need to load everything at the same time. The module only requires that it loads exactly what the user would expect to see at the time when the application first loads. The modules that experience lazy loading are only going to be loaded when the user navigates to their particular routes. Lazy loading allows for the improvement of the performance of key system applications. It also keeps the initial payload minimized, and these smaller type payloads may lead to a faster download speed. This would assist in lowering the resource cost, particularly when it comes to mobile networks. In the event that the user does not visit a section of the application, they may not download these resources at all. The concept of lazy loading in Angular requires the user to format the application in a particular manner. Each of the assets which are to be loaded must be added to their own module. It overcomes the problem of slow-loading of applications, which then assist with the loading time of the application. Lazy loading can be implemented using the following steps and methods:

• Update the route file • Install of the angular-router-loader and add the loader to the webpack configuration file.
• Define the lazy routes.
• Import the routes for the module.

19. What does it mean to have structural directive in Angular 2?

Structural directives can be used for the manipulation of DOM in Angular. Their obligation primarily concerns the HTML layout. Through the addition, removal, and manipulation of LMNs within angular, the reshaping of the structure of DOM is enabled. This structural directive is applied to the host element, along with the assistance of other directives. These directives do whatever they are meant to do concerning the host element and descendants. The structural directives may be easily recognized, and they can also delay the instantiation of the element or component. Additionally, these directives can be used for cosmetic effect or for the manual handling of the timing of the loading of components. The structural directives are then bound to a particular template. The two most common structural directives are ‘nglf’ and ‘ngFor’. As such, the process that is occurring in a structural directive is dynamic.

20. Can you tell me what is the difference between ActivatedRoute and RouterState?

• ActivatedRoute entails the information about a route that is linked with a component loaded in an outlet. RouterState, on the other hand, represents the state that the writer is.
• ActivatedRouterSnapchat is needed in order to traverse all of the activated routes. However, during navigation after redirect application, the router would create the RouterStateSnapshot.
• ActivatedRouteSnapshot has old data. When the route changes, ActivateRouteSnapshot has data stored from the previous route. The RouterState may care about the application components, or it might care more about the component arrangements.

21. What is routing?

Routing assists in directing users to different pages according to options chosen on the main page. Each chosen option allows that particular Angular Component to be rendered to the user.

22. What is CLI?

This stands for “Command Line Interface,” which is the interface used to create the Angular application. It may also assist in the construction of unit and end-to-end tests for the application.

23. How does routing work in Angular 2?

The angular application has a single instance of Router service. When the URL is altered, a corresponding Route is then matched from the routing configuration array. Upon successful matching, it applies redirects and the router constructs a tree of ActivatedRoute objects and has the current state of the router. Before redirection, the router is going to check if the new state would be permitted by running guards. The Route Guards are simply an interface method, which the router runs in order to check the route authorization. After the guard runs, it may resolve the route data and then activate the router state through instantiation of the needed components into the

24. What are the event emitters and how do they work within Angular 2?

Angular 2 does not have a bi-directional digest cycle. In Angular 2, any of the changes attained within the component are propagated from the present component to all of the children in hierarchy. In the event the change from one of the components needs to be reflected to any of the parent components in hierarchy, it is possible to emit the event through the use of Event Emitter API.

EventEmitter is class defined within @angular/core module that can be utilized by directives and components for emit custom events
@output () somethingChanged = new EventEmitter ();
You use somethingChanged.emit(value) method in order to emit the event. This can be done in the setter when the value is being changed within the class. This event emit may be subscribed by any of the components of the modules through the use of the subscribe approach. myObj.somethingChanged. subscribe(val) => this.myLocalMethod(val));

25. How would an engineer optimize an Angular 2 application for performance?

Optimization is dependent on the size and the type of the application and other factors. Though in general, there should be consideration for a number of points during the optimization of the Angular 2 application.

• Consideration of the AOT compilation.
• Make sure the application has been bundled and tree shaking has been done.
• Make certain the application does not have unnecessary import statements.
• Ensure that the 3rd party library, which has not yet been utilized, can be removed from the application.
• Have all of the dev-dependencies and the dependencies clearly separated.
• Loading ought to be considered as opposed to fully bundled app if the app size is more

26. How might it be possible to define the custom typing for one to avoid the editor warnings?

Most of the time, the 3rd party library comes with its .d.ts file for the type definition. Sometimes, there is a need to extend the existing type through giving more of the properties to it in the event that there is a need to define the additional types for avoiding the TypeScript warning. If it becomes necessary to extend the type definition for the external library, the user should not touch the node-modules of the existing typing folder. It should be possible to create a new folder referred to as ‘custom-typings’ and then keep the customized type definition within that new folder. When defining the typings for the JavaScript objects, there needs to be a definition of the interfaces and entity classes within the models folder of the respective modules of the particular application. For these cases, it is possible to define or to extend the types through the creation of a unique ‘.d.dts.’ file.

27. What is the Shadow Dom? How does it help Angular 2 function?

Shadow DOM is part of the HTML spec that allows the developers to encapsulate their HTML markup, JavaScript, and CSS Styles. The Shadow DOM, along with some of the other technologies, may provide the developers with the chance to build their 1st class tags, APIs, and web components like audio>tag. As a comprehensive collection, these APIs and new tags are called “Web Components.” The Shadow DOM allows for a better separation of concerns along with a smaller conflict in the scripts and styles of the other HTML DOM elements. Because the DOM appears to be static in nature, it qualifies as a candidate to be cached as it is not very accessible to the developer. The cached DOM may be rendered after within the browser providing a better performance. At the same time, the shadow DOM may be managed comparatively well while detecting the change in the Angular 2 application and re-painting of the view may be managed efficiently.

28. What is the Angular 2 hidden properties?

The hidden property within Angular 2 represents a special case.

• The property is more powerful and can be utilized for binding any of the properties of the elements.
• It is found to be the closest relation to ngshow and nghide.
• It sets the display property ‘display: none’.

29. What are the host decorators in Angular 2?

The host decorators within Angular 2 bind the properties of the components that have User Interface element values. The properties that are within a component class definition which are decorated with @HostBinding may be accessed in a template from the set property which is @HostBinding()title=’Our title'( whatever the title is).

30. Can you tell why decorator are and would be used within Angular 2?

The decorators can be utilized as an identifier of class or type of the object, which is created by the TypeScript. The Angular 2 identifies the class; below the decorator call as the definition of the class and would extend the decorator specific properties with class definition.

31. How do engineers handle errors or exceptions within Angular 2 applications?

Angular 2 applications are equipped with an error handling option. Errors in angular 2 can be handled through the inclusion of the ReactJS catch library, and later through the use of the catch function.

• The catch function used after adding the catch library includes the link to the error handler.
• In this error handler, the errors are then sent to the error console and thrown to effectively continue the implementation.
• This means that when an error occurs it is redirected to the error console of the web application.

32. What are the pros and cons of AoT compilation?


• A lesser number of Http Requests- if the application has not been bundled for the purpose of supporting lazy loading, (for each of the linked CSS and HTML) there is a separate request that goes to the server. The precompiled application in lines all of the templates and styles with components thus the number of the Http requests to the server is going to be lesser.
• The errors can be detected at build time; because the compilation happens before-hand, a lot of the compile time errors can be found and this allows for a better degree of stability for the application.


• There is no watch mode, so they have to be done manually while it compiles all of the files.
• It only works with HTML and CSS. The other file types require a previous build step.

author: patrick algrim
About the author

Patrick Algrim is an experienced executive who has spent a number of years in Silicon Valley hiring and coaching some of the world’s most valuable technology teams. Patrick has been a source for Human Resources and career related insights for Forbes, Glassdoor, Entrepreneur, Recruiter.com, SparkHire, and many more.


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