节流函数

throttle.js

function throttle(func, wait, options) {
  var timeout, context, args
  var previous = 0
  if (!options) options = {}

  var later = function() {
    previous = options.leading === false ? 0 : Date.now()
    timeout = null
    func.apply(context, args)
    if (!timeout) context = args = null
  }

  var thorttled = function() {
    var now = Date.now()
    if (!previous && options.leading === false) previous = now
    var remaining = wait - (now - previous)
    context = this
    args = arguments

    // 如果没有剩余的时间了或者你改了系统时间
    if (remaining <= 0 || remaining > wait) {
      if (timeout) {
        clearTimeout(timeout)
        timeout = null
      }
      previous = now
      func.apply(context, args)
      if (!timeout) context = args = null
    } else if (!timeout && options.trailing !== false) {
      timeout = setTimeout(later, wait)
      console.log(2)
    }
  }

  return thorttled
}