一篇文章弄懂防抖和节流

防抖：

        当事件被触发时，n秒后执行回调函数，如果在这个时间（n秒）内，事件被再次触发，则重新计时。

应用场景：

1.scroll事件滚动触发

2.搜索框输入查询

3.表单验证

4.按钮提交事件

5.浏览器窗口缩放，resize事件

6.等等影响体验和性能的高频动作......

function debounce(func, wait, immediate) {
  let timeout, result;
  let decounced = function() {
    let context = this;
    let args = arguments;
    if(timeout)clearTimeout(timeout)
    if(immediate) {
      let callNow = !timeout;
      timeout = setTimeout(() => {
        timeout = null;
      }, wait);
      if (callNow) result = func.apply(context, args)
    }else {
      timeout = setTimeout(function() {
        result = func.apply(context, args)
      }, wait);
    }
    return result;
  }
  decounced.cancel = function name() {
    clearTimeout(timeout);
    timeout = null;
  }
  return decounced;
}







lodash 源码
function debounce(func, wait, options) {
  let lastArgs,
    lastThis,
    maxWait,
    result,
    timerId,
    lastCallTime

  let lastInvokeTime = 0
  let leading = false
  let maxing = false
  let trailing = true

  // Bypass `requestAnimationFrame` by explicitly setting `wait=0`.
  const useRAF = (!wait && wait !== 0 && typeof root.requestAnimationFrame === 'function')

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

  function invokeFunc(time) {
    const args = lastArgs
    const thisArg = lastThis

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

  function startTimer(pendingFunc, wait) {
    if (useRAF) {
      root.cancelAnimationFrame(timerId)
      return root.requestAnimationFrame(pendingFunc)
    }
    return setTimeout(pendingFunc, wait)
  }

  function cancelTimer(id) {
    if (useRAF) {
      return root.cancelAnimationFrame(id)
    }
    clearTimeout(id)
  }

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

  function remainingWait(time) {
    const timeSinceLastCall = time - lastCallTime
    const timeSinceLastInvoke = time - lastInvokeTime
    const timeWaiting = wait - timeSinceLastCall

    return maxing
      ? Math.min(timeWaiting, maxWait - timeSinceLastInvoke)
      : timeWaiting
  }

  function shouldInvoke(time) {
    const timeSinceLastCall = time - lastCallTime
    const timeSinceLastInvoke = time - lastInvokeTime

    // 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 === undefined || (timeSinceLastCall >= wait) ||
      (timeSinceLastCall < 0) || (maxing && timeSinceLastInvoke >= maxWait))
  }

  function timerExpired() {
    const time = Date.now()
    if (shouldInvoke(time)) {
      return trailingEdge(time)
    }
    // Restart the timer.
    timerId = startTimer(timerExpired, remainingWait(time))
  }

  function trailingEdge(time) {
    timerId = undefined

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

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

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

  function pending() {
    return timerId !== undefined
  }

  function debounced(...args) {
    const time = Date.now()
    const isInvoking = shouldInvoke(time)

    lastArgs = args
    lastThis = this
    lastCallTime = time

    if (isInvoking) {
      if (timerId === undefined) {
        return leadingEdge(lastCallTime)
      }
      if (maxing) {
        // Handle invocations in a tight loop.
        timerId = startTimer(timerExpired, wait)
        return invokeFunc(lastCallTime)
      }
    }
    if (timerId === undefined) {
      timerId = startTimer(timerExpired, wait)
    }
    return result
  }
  debounced.cancel = cancel
  debounced.flush = flush
  debounced.pending = pending
  return debounced
}

节流：

  如果你持续触发事件，每隔一段时间，只执行一次事件。

function throttle(func, wait, options) {
  let leading = true
  let trailing = true

  if (typeof func !== 'function') {
    throw new TypeError('Expected a function')
  }
  if (isObject(options)) {
    leading = 'leading' in options ? !!options.leading : leading
    trailing = 'trailing' in options ? !!options.trailing : trailing
  }
  return debounce(func, wait, {
    leading,
    trailing,
    'maxWait': wait
  })
}

 应用场景：

1.dom元素的拖拽功能

2.射击游戏

3.计算鼠标移动的距离

4.监听scroll滚动事件