Little note on pure functions

pure.js

// A function is only pure if, given the same input, it will always produce the same output.
const highpass = (cutoff, value) => value >= cutoff;

highpass(5, 123); // true
highpass(5, 6);   // true
highpass(5, 18);  // true
highpass(5, 5);   // true
highpass(5, 1);   // false
highpass(5, 3);   // false
highpass(5, 4);   // false