Function warnNonPresent

static/vuejs/vue.esm.js:1466–1473

(target, key)

  );

  var warnNonPresent = function (target, key) {
    warn(
      "Property or method \"" + key + "\" is not defined on the instance but " +
      "referenced during render. Make sure to declare reactive data " +
      "properties in the data option.",
      target
    );
  };

  var hasProxy =
    typeof Proxy !== 'undefined' &&