函数节流 throttle

事件被触发 n 秒之内只会执行一次事件处理函数

function throttle (fn, delay) {
  var t = null,
      begin = new Date().getTime();
  return function () {
    var _self = this,
        args = arguments;
    var cur = new Date().getTime();
    clearTimeout(t);
    if (cur - begin >= delay) {
      fn.apply(_self, args);
      begin = cur;
    } else {
      t = setTimeout(function () {
        fn.apply(_self, args);
      }, delay);
    }
  }
}