code: function initRender (vm) {
    vm._vnode = null; // the root of the child tree
    vm._staticTrees = null;
    var parentVnode = vm.$vnode = vm.$options._parentVnode; // the placeholder node in parent tree
    var renderContext = parentVnode && parentVnode.context;
    /**
     * react-vue change
     */
    // vm.$slots = resolveSlots(vm.$options._renderChildren, renderContext)
    vm.$scopedSlots = emptyObject;
    // bind the createElement fn to this instance
    // so that we get proper render context inside it.
    // args order: tag, data, children, normalizationType, alwaysNormalize
    // internal version is used by render functions compiled from templates
    vm._c = function (a, b, c, d) { return createElement(vm, a, b, c, d, false); };
    // normalization is always applied for the public version, used in
    // user-written render functions.
    vm.$createElement = function (a, b, c, d) { return createElement(vm, a, b, c, d, true); };
  }
docs: Runtime helper for v-once.
  Effectively it means marking the node as static with a unique key.
   /*