Function add$1

static/vuejs/vue.common.js:5868–5887

(
  event,
  handler,
  once,
  capture
)

var target$1;

function add$1 (
  event,
  handler,
  once,
  capture
) {
  if (once) {
    var oldHandler = handler;
    var _target = target$1; // save current target element in closure
    handler = function (ev) {
      var res = arguments.length === 1
        ? oldHandler(ev)
        : oldHandler.apply(null, arguments);
      if (res !== null) {
        remove$2(event, handler, capture, _target);
      }
    };
  }
  target$1.addEventListener(event, handler, capture);
}

function remove$2 (
  event,