code: function bindFunc(obj, method, observer) {
      const oldFn = obj[method]
      obj[method] = function(target) {
          if (observer) {
              observer.call(this, target, {
                  [method]: true,
              })
          }
          if (oldFn) {
              oldFn.call(this, target)
          }
      }
  }
docs: bind func to obj