An ES6 implementation of the throttle function. "Throttling enforces a maximum number of times a function can be called over time. As in 'execute this function at most once every 100 milliseconds.'" - CSS-Tricks (https://css-tricks.com/the-difference-between-throttling-and-debouncing/)

throttle.js

function throttle(callback, wait, context = this) {
  let timeout = null 
  let callbackArgs = null
  
  const later = () => {
    callback.apply(context, callbackArgs)
    timeout = null
  }
  
  return function() {
    if (!timeout) {
      callbackArgs = arguments
      timeout = setTimeout(later, wait)
    }
  }
}

/**
 * Normal event
 * event      | |      |
 * time     ----------------
 * callback   | |      |
 * 
 * Call search at most once per 300ms while keydown
 * keydown     | |     |  |
 * time     -----------------
 * search          |       | 
 *             |300|   |300|
 */
 
/** usage
const handleKeydown = throttle((e) => {
  console.log(e.target.value)
}, 300)

input.addEventListener('keydown', handleKeydown)
*/