lib/index.esm.js
function addDelegate(el, selector, type, handler) {
  var capture = arguments.length > 4 && arguments[4] !== undefined ? arguments[4] : false;

  if (capture !== undefined && !isBoolean(capture) && supportsPassive) {
    capture = { passive: true };
  }
  var handlerWrap = function handlerWrap(e) {
    var targetElsArr = findParents(e.target || e.srcElement, el, true);
    var targetElArr = query(selector, el, true);
    var retEl = void 0;
    if (targetElArr.find) {
      retEl = targetElArr.find(function (seEl) {
        return targetElsArr.find(function (tgEl) {
          return seEl === tgEl;
        });
      });
    } else {
      // Fixed IE11 Array.find not defined bug
      targetElArr.forEach(function (seEl) {
        return !retEl && targetElsArr.forEach(function (tgEl) {
          if (!retEl && seEl === tgEl) {
            retEl = tgEl;
          }
        });
      });
    }
    retEl && handler.apply(retEl, arguments);
  };
  /* 将包装后的方法记录到缓存中 */
  addEventCache(el, type + '_delegate_' + selector, handler, handlerWrap);
  el.addEventListener(type, handlerWrap, capture);
}
function addDelegate(el, selector, type, handler) {
  var capture = arguments.length > 4 && arguments[4] !== undefined ? arguments[4] : false;

  if (capture !== undefined && !isBoolean(capture) && supportsPassive) {
    capture = { passive: true };
  }
  var handlerWrap = function handlerWrap(e) {
    var targetElsArr = findParents(e.target || e.srcElement, el, true);
    var targetElArr = query(selector, el, true);
    var retEl = void 0;
    if (targetElArr.find) {
      retEl = targetElArr.find(function (seEl) {
        return targetElsArr.find(function (tgEl) {
          return seEl === tgEl;
        });
      });
    } else {
      // Fixed IE11 Array.find not defined bug
      targetElArr.forEach(function (seEl) {
        return !retEl && targetElsArr.forEach(function (tgEl) {
          if (!retEl && seEl === tgEl) {
            retEl = tgEl;
          }
        });
      });
    }
    retEl && handler.apply(retEl, arguments);
  };
  /* 将包装后的方法记录到缓存中 */
  addEventCache(el, type + '_delegate_' + selector, handler, handlerWrap);
  el.addEventListener(type, handlerWrap, capture);
}
为HTML元素添加事件代理
@param {HTMLElement} el 目标元素
@param {String} selector 要被代理的元素
@param {String} type 事件名称
@param {Function} handler 处理函数
@param {Boolean} capture 是否在捕获阶段监听