Coding Challenge Practice - Question 117

The task is to implement an enhanced debounce which has an option to invoke right away or after a delay.

The boilerplate code

function debounce(func, wait, option = {leading: false, trailing: true}) {
  // your code here
}

Keep track of the delay required and the latest call data

let timer = null;
let lastArgs;
let lastThis;

When the function is called, clear any existing timer and start a new one

return function(...args) {
lastArgs = args;
lastThis = this;

if(timer) clearTimeout(timer);

If there is no active timer, the function executes immediately on first call.

const shouldCallNow = option.leading && !timer

if(shouldCallNow) {
func.apply(lastThis, lastArgs)
lastArgs = lastThis = null;
}

If there is a timer, the function executes after a waiting period expires

timer = setTimeout(() => {
timer = null;
if(option.trailing && lastArgs) {
func.apply(lastThis, lastArgs)
lastArgs = lastThis = null;
}
}, wait)

The final code

function debounce(func, wait, option = {leading: false, trailing: true}) {
  // your code here
  let timer = null;
  let lastArgs;
  let lastThis;

  return function(...args) {
    lastArgs = args;
    lastThis = this;

    const shouldCallNow = option.leading && !timer;

    if(timer) clearTimeout(timer);

    timer = setTimeout(() => {
      timer = null;

      if(option.trailing && lastArgs) {
        func.apply(lastThis, lastArgs)
        lastArgs = lastThis = null;
      }
    }, wait)
    if(shouldCallNow) {
      func.apply(lastThis, lastArgs);
      lastArgs = lastThis = null;
    }
  }
}

That's all folks!