20 Angular Pipe Interview Questions and Answers

Angular pipes are a way to transform data in an Angular template. They are used to format data for display, and can be used to create custom pipes. When applying for a position that involves Angular, it is likely that you will be asked questions about pipes. In this article, we review the most common Angular pipe questions and provide tips on how to answer them.

Angular Pipe Interview Questions and Answers

Here are 20 commonly asked Angular Pipe interview questions and answers to prepare you for your interview:

1. What are pipes in Angular?

Pipes are a feature in Angular that allow you to transform data before it is displayed in the template. This is useful for things like formatting dates, currencies, and other data. There are many built-in pipes in Angular, and you can also create your own custom pipes.

2. Can you explain the difference between a pure and impure pipe in Angular?

A pure pipe is only re-evaluated when either the input to the pipe changes or the pipe itself is destroyed. An impure pipe is re-evaluated every time change detection runs.

3. How can you create custom pipes in Angular?

You can create custom pipes in Angular by using the @Pipe decorator. This decorator allows you to define a pipe and its name, as well as set any arguments that the pipe may take. You can then use this pipe in your templates just like any other built-in pipe.

4. Can you explain what a stateful pipe is? Why would you need one?

A stateful pipe is a pipe that maintains state between invocations. This is necessary for certain types of pipes that need to keep track of data across multiple invocations, such as a sorting pipe that needs to remember the last sort order so that it can toggle between ascending and descending.

5. Is it possible to pass parameters to a pipe in Angular? If yes, then how?

Yes, it is possible to pass parameters to a pipe in Angular. In order to do so, you need to specify the parameters you want to pass in within the pipe’s signature. For example, if you want to pass in a string and an integer, you would do so like this:

myPipe(string: string, integer: number) {
// …
}

6. What is the usage of the “async” pipe in Angular?

The async pipe is used to automatically subscribe and unsubscribe from an observable in Angular. This is helpful in cases where you are using observables to fetch data from a remote source, as it will handle the subscription automatically.

7. Can you give me an example of using a special type of pipe called async pipe?

Async pipe is used when you have a data stream that you want to automatically unsubscribe from when the component is destroyed. This is useful for when you are using observables or RxJS in your Angular application. For example, you could use the async pipe to automatically unsubscribe from a timer observable when the component is destroyed.

8. What are some advantages of using pipes in Angular applications?

Pipes are a great way to make your Angular application more modular and efficient. By breaking up your application into smaller pieces, you can more easily reuse code and make changes without affecting the entire application. Pipes also make it easy to format data for display, which can be a big help when working with large data sets.

9. When should you use a pipe instead of a filter in an Angular application?

Pipes are used for transforming data before it is displayed to the user, while filters are used for formatting data that is already displayed to the user. If you need to modify the data in some way before it is displayed, then you should use a pipe. If you just need to format the data that is already being displayed, then you should use a filter.

10. What happens if a function or method returns a value with multiple arguments?

Angular pipes can only handle a single return value. If a function or method returns multiple values, then Angular will only take the first value and ignore the rest.

11. Can you explain what a boundary value problem is?

A boundary value problem is a mathematical problem in which the solution is constrained by one or more boundary conditions. In other words, it is a problem in which the solution must satisfy certain conditions at the boundary of the domain.

12. What do you understand by bitwise operations in programming languages like JavaScript?

Bitwise operations are a type of operation that can be performed on integer data types that treat the data as a series of bits, rather than as a whole number. These operations are typically used for bitwise manipulation, such as setting or clearing individual bits, or for performing Boolean operations on groups of bits.

13. What’s your understanding of hoisting in JavaScript?

Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope before code execution. So, in essence, all variables and functions are available in their scope before code execution.

14. What is currying in context with JavaScript?

Currying is a technique for creating functions that can accept partial arguments. This allows you to create new functions from existing functions, without having to write any new code. In the context of Angular, this can be used to create custom pipes that only take the arguments that you need.

15. What is partial application in context with JavaScript?

Partial application is a technique for creating new functions from existing functions, by “pre- filling” some of the arguments. This can be useful when you want to create a new function that is similar to an existing function, but with some of the arguments already set.

16. What is memorization? Do you think memoization helps improve performance in JavaScript code?

Memorization is a technique used to improve performance in JavaScript code by caching the results of function calls and reusing those results when the same function is called again. This can help improve performance because the function doesn’t need to be executed again, and the cached results can be used instead.

17. What is the importance of decorators in JavaScript? Give an example of how they can be used.

Decorators are a feature in JavaScript that allows you to modify the behavior of a class or object. They are used in Angular to add additional functionality to components, directives, and pipes. For example, you can use a decorator to specify the template that should be used for a component, or to specify the function that should be called when a certain event occurs.

18. What is the significance of the yield keyword in JavaScript generators?

The yield keyword is used to pause and resume a generator function. When a generator function encounters a yield keyword, it pauses execution and returns a value. The value of the yield keyword is the value that is returned to the caller. When the caller calls the next() method on the generator, execution resumes and the next value is returned.

19. Is there any way to stop executing a generator? If yes, then how?

Yes, there is a way to stop executing a generator. You can use the return keyword to stop the generator function from continuing.

20. What are some differences between Promises and Observables? Which one is better for certain situations?

Promises are a way to handle asynchronous operations in JavaScript, while observables are a way to handle asynchronous operations in Angular. Promises are generally better for one-off operations, while observables are better for handling multiple, concurrent operations.