Pure function example with JavaScript

pureFunctions.js

// impure (using side effect instead of return value)
function addTaco(array) {
   array.push("taco");
}

// impure (using shared variable instead of argument)
function addTaco() {
   return [...globalArray, "taco"];
}

// pure
function addTaco(array) {
   return [...array, "taco"];
}