Debouncing examples

debounce.js

const debounce1 = (fn, delay) => {
  let timer = null;
  return function (...args) {
      const context = this;
      timer && clearTimeout(timer);
      timer = setTimeout(() => {
          fn.apply(context, args);
      }, delay);
  };
}

const debounce2 = function(fn, delay) {
  let timer;

  return function() {
    const context = this;
    const args = arguments;
    clearTimeout(timer);
    timer = setTimeout(() => fn.apply(context, args), delay);
  };
};

const debounce3 = function(fn, delay, immediate) {
  let timer;
  
  return function() {
    const context = this;
    const args = arguments;
    const callNow = immediate && !timer;
    
    clearTimeout(timer);
    
    timer = setTimeout(function() {
      timer = null;
      
      if (!immediate) {
        fn.apply(context, args);
      }
    }, delay);
    
    if (callNow) {
      fn.apply(context, args);
    }
  };
};