Pure Functions for Dummies

What is a pure function

Functions that produce no side effects and have the same output given the same input are called "pure".

You can easily check if a function is pure:

• Pure functions always return the same output given the same input
• Pure functions have no side-effects

Some examples:

Pure Function:

function triple(value) {
  return value * 3;
}

Impure Function:

function getCurrentTime() {
  return new Date().toLocaleTimeString();
}

The advantages of pure functions

• Easier to test, because they are deterministic (Same input = Same output)
• Portable, pure functions are not dependent on their environment and therefore can be more easily reused
• Makes functions memoizable
• Easier to refactor, because you don't have to worry about side effects