What is referential transparency?

An expression in javascript that can be replaced by its value without affecting the behaviour of the program is called referential transparency. Pure functions are referentially transparent.

const add = (x, y) => x + y;
const multiplyBy2 = (x) => x * 2;

//Now add (2, 3) can be replaced by 5.

multiplyBy2(add(2, 3));