What is a thunk function

A thunk is just a function which delays the evaluation of the value. It doesn’t take any arguments but gives the value whenever you invoke the thunk. i.e, It is used not to execute now but it will be sometime in the future. Let's take a synchronous example,

const add = (x, y) => x + y;

const thunk = () => add(2, 3);

thunk(); // 5