      function oneTimeListener(value, old, scope) {
        lastValue = value;
        if (isFunction(listener)) {
          listener(value, old, scope);
        }
        if (isDefined(value)) {
          scope.$$postDigest(function() {
            if (isDefined(lastValue)) {
              unwatch();
            }
          });
        }
      }
The software constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.