Simple example of recursion - web dev interview, discussion

simple-recursion.js

// e.g. "write a simple function that logs out the factor of a given number"
// input '4' should return '24' since 4 * 3 * 2 * 1 = 24
// input '6' should return '720' etc...

// First, discuss and consider the basic utility of a `while` loop
function factor(number) {
  let result = 1;
  let count = number;
  while (count > 1) {
    result *= count;
    count--;
  }
  return result;
}

console.log('should be 24', factor(4));
console.log('should be 720', factor(6));

// alternatively just ask for a countdown function
function countdownLoop(value) {
  while (value > 0) {
    console.log(value--);
  }
  return value;
}

console.log(countdownLoop(10));

// discuss some downsides to a loop...
// - state that's being maintained / changed in that function 
// ... how can we reproduce the functionality of a while loop without creating all that state

// recursion countdown
// - discuss terminal condition 
function countdownRecursively(value) {
  if (value > 0) {
    console.log(value);
    return countdownRecursively(value - 1);
  } else {
    return value;
  }
}

const terminal = countdownRecursively(10);
console.log(terminal);

// Now the recursive function for getting a factorial
function factorial(number) {
  if (number <= 0) {
    return 1;
  } else {
    return (number * factorial(number - 1));
  }
}

console.log(factorial(6));

// discussion points, value of using recursive functions is clean code that you get. 
// We're performing a stateless operation. 
// We're not changing the value of any variables along the way. 
// We're having no side effects outside of the functions, so nothing outside is being changed. 
// We're testing for the terminal condition first. And that allows us to 
// exit quickly and cleanly from our recursive function.

// downsides of recursion
// - high memory usage of deep recursion
// - code difficult to read for those unfamiliar with recursion