Impure vs Pure functions

Reena Lakra

7y1.4kAngular

What is the difference between impure and pure functions?

3 Replies

Know the answer? Post it — somebody with the same question will find it here.

Mahesh Verma7y ago
Accepted answer
Hello Reena,

Impure functions are those functions which modifying their argument like

function calculate(input) {
input.count++;
}

In the above function, if the initial value of count is 0 and we call this function 10 times then the value of count is 10.

However, on the other side, if we talk about Pure Functions, we cannot modify the value, we can return a new value each time, like

function calculate(input){
return {count : input.count+1};
}

Hope, this code will help you to understand difference between them.
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Muthu Kumar7y ago
Here is an alternative example and description for Pure and Impure Functions

https://stackoverflow.com/questions/22395311/difference-between-pure-and-impure-function
https://www.quora.com/What-is-the-difference-between-a-pure-and-an-impure-function

This solution has been mentioned above url,

Characteristics of Pure Function:
1. The return value of the pure functions solely depends on its arguments Hence, if you call the pure functions with the same set of arguments, you will always get the same return values.
2. They do not have any side effects like network or database calls
3. They do not modify the arguments which are passed to them
Characterisitcs of Impure functions
1. The return value of the impure functions does not solely depend on its arguments Hence, if you call the impure functions with the same set of arguments, you might get the different return values For example, Math.random(), Date.now()
2. They may have any side effects like network or database calls
3. They may modify the arguments which are passed to them
function impureFunc(value){

  return Math.random() * value;

}



function pureFunc(value){

  return value * value;

}



var impureOutput = [];

for(var i = 0; i < 5; i++){

   impureOutput.push(impureFunc(5));

}



var pureOutput = [];

for(var i = 0; i < 5; i++){

   pureOutput.push(pureFunc(5));

}



console.log("Impure result: " + impureOutput); // result is inconsistent however input is same.



console.log("Pure result: " + pureOutput); // result is consistent with same input
0
Jignesh Kumar7y ago
Hi Reena,

Please find below links,
https://toddmotto.com/pure-versus-impure-functions
https://blog.angularindepth.com/the-essential-difference-between-pure-and-impure-pipes-and-why-that-matters-999818aa068
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