Pure And Impure Functions in Javascript

Pure Functions

A pure function in Javascript is one that given the same input will always return the same output and does not have any observable side effect.

This means that it does not depend on or change any state outside of the function and will always return the same output value for the same input.

Example

add = (a, b) => {
return a+b;
}
console.log(add(3,4)); //7

Impure Functions

The outcome of an impure function on the other hand depends on any change outside of the function and will not return the same output value for the same input.

Example

let minimum = 21;
let checkAge = function(age){
return age > minimum;
}
console.log(checkAge(22)); //True

In the above example, the outcome of the program depends on the value assigned to the minimum variable. If that variable changes, the function will not return the same output value even if the input remains constant.

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