Frontend Interview Question | What are Pure Functions? | SideEffects | Javascript Interview

Hello Everyone
In this session, we will learn about Pure Functions in Javascript and this is one of the asked question in Interview .

What are Pure Functions?
Function that produces the same output for the same input. It means it returns the same result when you pass the same arguments. A pure function shouldn't have any side effects to change the expected output

We need to make sure functions are,

Predictable: It produces a predictable output for the same inputs.
Readable: Anyone reading the function as a standalone unit can understand its purpose completely.
Reusable: Can reuse the function at multiple places of the source code without altering its and the caller's behavior.
Testable: We can test it as an independent unit.

What is SideEffect ?
Any operation that is not directly related to the final output of the function is called a Side Effect

A few more classic cases of the side effects are,

1)Mutating(changing) the input itself.
2) Querying/Updating DOM
3 )Logging(even in the console)
4) Making an XHR/fetch call.

Check another important interview Question

Check video on Recursion

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[buntykhipal]

this video helped me a lot to learn difference between pure and impure function
thank for making video

[gyanendra_chaubey]

Your questions are awesome and you are doing great job. Is it possible for you to add more FE questions especially tricky ones like the one (async + settimeout + promises one). Anyways thank's for what ever you have posted till date.

[BrijeshSingh-dpku]

Hi Nisha, thanks for sharing.. where you work?