浅谈JavaScript节流和防抖函数

let debounce = function(f, interval = 1000) {
 let handler = null;
 return function() {
  if (handler) {
  clearTimeout(handler);
  }
  let arg = arguments;
  handler = setTimeout(function() {
  f.apply(this, arg);
  clearTimeout(handler);
  }, interval)
 }
 }

let input = document.querySelector('#input');
 input.addEventListener('input', debounce(function(e) {
 console.log("您的输入是",e.target.value)
 }))

let throttle = function(f,gap = 300){
  let lastCall = 0;
  return function(){
  let now = Date.now();
  let ellapsed = now - lastCall;
  if(ellapsed < gap){
   return
  }
  f.apply(this,arguments);
  lastCall = Date.now();
  }
 }

document.addEventListener('scroll', throttle(function (e) {
 // 判断是否滚动到底部的逻辑
 console.log(e,document.documentElement.scrollTop);
 }));

$(window).on('scroll', _.debounce(doSomething, 200));

function debounce(func, wait, options) {
 var lastArgs,
  lastThis,
  result,
  timerId,
  lastCallTime = 0,
  lastInvokeTime = 0,
  leading = false,
  maxWait = false,
  trailing = true;

 if (typeof func != 'function') {
  throw new TypeError(FUNC_ERROR_TEXT);
 }
 wait = wait || 0;
 if (isObject(options)) {
  leading = !!options.leading;
  maxWait = 'maxWait' in options && Math.max((options.maxWait) || 0, wait);
  trailing = 'trailing' in options ? !!options.trailing : trailing;
 }

 function invokeFunc(time) {
  var args = lastArgs,
  thisArg = lastThis;

  lastArgs = lastThis = undefined;
  lastInvokeTime = time;
  result = func.apply(thisArg, args);
  return result;
 }

 function leadingEdge(time) {
  console.log("leadingEdge setTimeout")
  // Reset any `maxWait` timer.
  lastInvokeTime = time;
  // Start the timer for the trailing edge.
  timerId = setTimeout(timerExpired, wait);
  // Invoke the leading edge.
  return leading ? invokeFunc(time) : result;
 }

 function remainingWait(time) {
  var timeSinceLastCall = time - lastCallTime,
  timeSinceLastInvoke = time - lastInvokeTime,
  result = wait - timeSinceLastCall;
  console.log("remainingWait",result)
  return maxWait === false ? result : Math.min(result, maxWait - timeSinceLastInvoke);
 }

 function shouldInvoke(time) {
  console.log("shouldInvoke")
  var timeSinceLastCall = time - lastCallTime,
  timeSinceLastInvoke = time - lastInvokeTime;
  console.log("time",time,"lastCallTime",lastCallTime,"timeSinceLastCall",timeSinceLastCall)
  console.log("time",time,"lastInvokeTime",lastInvokeTime,"timeSinceLastInvoke",timeSinceLastInvoke)
  console.log("should?",(!lastCallTime || (timeSinceLastCall >= wait) ||
  (timeSinceLastCall < 0) || (maxWait !== false && timeSinceLastInvoke >= maxWait)))
  // Either this is the first call, activity has stopped and we're at the
  // trailing edge, the system time has gone backwards and we're treating
  // it as the trailing edge, or we've hit the `maxWait` limit.
  return (!lastCallTime || (timeSinceLastCall >= wait) ||
  (timeSinceLastCall < 0) || (maxWait !== false && timeSinceLastInvoke >= maxWait));
 }

 function timerExpired() {
  console.log("timerExpired")
  var time = Date.now();
  if (shouldInvoke(time)) {
  return trailingEdge(time);
  }
  console.log("Restart the timer.",time,remainingWait(time))
  // Restart the timer.
  console.log("timerExpired setTimeout")
  timerId = setTimeout(timerExpired, remainingWait(time));
 }

 function trailingEdge(time) {
  clearTimeout(timerId);
  timerId = undefined;

  // Only invoke if we have `lastArgs` which means `func` has been
  // debounced at least once.
  console.log("trailing",trailing,"lastArgs",lastArgs)
  if (trailing && lastArgs) {
  return invokeFunc(time);
  }
  lastArgs = lastThis = undefined;
  return result;
 }

 function cancel() {
  if (timerId !== undefined) {
  clearTimeout(timerId);
  }
  lastCallTime = lastInvokeTime = 0;
  lastArgs = lastThis = timerId = undefined;
 }

 function flush() {
  return timerId === undefined ? result : trailingEdge(Date.now());
 }

 function debounced() {
  var time = Date.now(),
  isInvoking = shouldInvoke(time);
  console.log("time",time);
  console.log("isInvoking",isInvoking);
  lastArgs = arguments;
  lastThis = this;
  lastCallTime = time;

  if (isInvoking) {
  if (timerId === undefined) {
   return leadingEdge(lastCallTime);
  }
  // Handle invocations in a tight loop.
  clearTimeout(timerId);
  console.log("setTimeout")
  timerId = setTimeout(timerExpired, wait);
  return invokeFunc(lastCallTime);
  }
  return result;
 }
 debounced.cancel = cancel;
 debounced.flush = flush;
 return debounced;
 }