JavaScript Functions Interview Questions

1. Define a named function in JavaScript. How is it beneficial?

A named function is a type of function declaration if it appears in the statement. It can be defined using the keyword ‘function’. These are very helpful in finding what particular function caused errors in the program. These make the code more understandable and accessible. Also, they enhance readability.

2. What are the steps to create a function in JavaScript?

Syntax to write a function in JavaScript:

Function name (parameters)
{
Code
}

3. What are the pop-up boxes in JavaScript?

The three various pop-up boxes are: Alert box, Confirm box, and Prompt box.

Alert box - Used to throw a message to the user.

Confirm - Used to verify something from the user

Prompt - Used to get a value from the user, before entering another page

4. What are the function parameter rules?

The function definition does not specify the data type for the parameter.
Never perform type checking on the arguments that are passed.
The number of arguments received should not be checked.

6. What is the use of compareFunction while sorting arrays in JavaScript?

The compareFunction helps define the sort order. In case the function is not used while sorting the array, the elements are converted into a string, then they are sorted according to the point value of each Unicode’s character. The following example will further explain the use.

let number = [1, 2, 5, 3, 4]; number.sort((a, b) => b - a); console.log(number); // [5, 4, 3, 2, 1]

7. What is the use of some method in arrays?

The some() method is used to test if at least one element in the array can pass the test implemented by the provided function. It returns a boolean value.

8. How to create a specific number of copies of a string in JavaScript?

The repeat() method is for the purpose of constructing and returning a new string with the exact number of copies as specified (a concatenated one). This method of copying has been added to the ECMAScript 2015 specification list.

9. Against a regular expression, how to return all matching strings?

The matchAll() method can be used for the purpose. Against any regular expression, matchAll() can return an iterator of all such matching strings.

10. What is a thunk function?

A thunk function delays the evaluation of the value. Thunk does not take arguments but gives value whenever invoked i.e, It is used to avoid prompt execution but perform in the near future. Let’s take an example,

const add = (x,y) => x + y; const thunk = () => add(2,3); thunk()

11. What is the difference between Function constructors and function declaration?

The functions created using function constructors are created in the global space but not closures to their creation contexts i.e. these functions can access only. Whereas function declarations can be accessed in outer function variables(closures) too.

12. What is an async function?

An async function is a function that is declared with the async keyword which enables an asynchronous and promise-based behavior to be written in a clean style by avoiding promise chains. Async functions can either contain zeroes or more await expressions.

It is somewhat like syntax sugar over ES2015 promises and generators.

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