How to understand trampoline in JavaScript?

Question

Here is the code:

function repeat(operation, num) {
  return function() {
    if (num <= 0) return
    operation()
    return repeat(operation, --num)
  }         


        

Answer 1

The while loop will keep running until the condition is falsy.

fn && typeof fn === 'function' will be falsy either if fn itself is falsy, or if fn is anything other than a function.

The first half is actually redundant, since falsy values are also not functions.