throttle & debounce from scratch

throttle-debounce.js

function throttle(fn, delay) {
  let startTime = 0

  return function (...args) {
    const now = Date.now()
    // if not in progress
    if (startTime === 0) {
      startTime = now
    }

    if (now - startTime >= delay) {
      startTime = 0      
      return fn(...args)
    }
  }
}

function debounce(fn, delay) {
  let storedArgs = []
  let timerId = 0

  return function(...args) {
    storedArgs = args
    
    if (timerId) {
      clearTimeout(timerId)
    }
    
    timerId = setTimeout(later, delay)
    
    function later() {
      timerId = 0
      
      return fn(...storedArgs)
    }    
  }  
}