Function once

packages/zone.js/lib/common/promise.ts:119–131

()

    }

    const once = function () {
      let wasCalled = false;

      return function wrapper(wrappedFunction: Function) {
        return function () {
          if (wasCalled) {
            return;
          }
          wasCalled = true;
          wrappedFunction.apply(null, arguments);
        };
      };
    };

    const TYPE_ERROR = 'Promise resolved with itself';
    const CURRENT_TASK_TRACE_SYMBOL = __symbol__('currentTaskTrace');