JavaScript Closure Interview Questions

A closure in JavaScript is known as JavaScript closure. It makes it possible for a function to have "private" variables. JavaScript closure is used to control what is and isn't in scope in a particular function, along with which variables are shared between sibling functions in the same containing scope.

There are several advantages of using closures in JavaScript. Some of them are:

• Closure enables the use of nested functions that are used to get the values created in the execution context of that of the parent function.
• They can prove as a perfect solution while solving a problem of hierarchy in any program.
• They have huge importance as far as functional programming is concerned. It solves the for loop problem of functional programming.
• It is also used to simulate private scope for variables.

Whenever you create a function within another function, then the inner function is closure. This closure is usually returned so you can use the outer function’s variables at a later time. Whereas a scope in JavaScript defines what variables you have access to. There are two kinds of scope – global scope and local scope.

A Deep copy is a process in which the copying process occurs recursively which means all of the values of the new variable are copied and disconnected from the original variable.

An object that is able to produce a single value sometime in the future is known as Promise. The single value may either be a resolved value, or it can be a reason that it’s not resolved. There can be three states in which Promise can be:

• Fulfilled
• Reject
• Pending

There can be callbacks that can be attached to handle the fulfilled value or the rejection’s reason, this can be done by the Promise users.