The template tag is meant to wrap multiple elements like:

<template v-for="item in list">
   <span>{{ item.key }}</span>
  <span> {{ item.name }}</span>
</template>

In your case you should simply use <span v-for="item in list"></span> to wrap the text nodes

I know.
but the real scene in my code is more complex than this demo. I need to wrap multiple elements in a template tag, but the output is undefined.
and it works all right in v2.1.6.
it seems all v-for directive inside a template tag output undefined if there's child component with props bind before the tag.
like this:

<component :list="list"></component>
<template v-if="ready">
        <div v-for="item of items">{{item.name}}</div> <!--here undefined-->
        <!-- ...other -->
</template>

and is this the expected behavior?

at least the template like:

<component :list="list"></component>
<template v-for="(item,index) of list2">
    <div>{{index}}</div>
    <div>{{item.name}}</div>
</template>

works wrong.

and sometimes the v-for directive inside a template tag also output undefined, and works ok if I modified some code. I really don't know how it happen;

Does happen in 2.1.7: https://jsfiddle.net/14dtfh51/8/
Does not happen in 2.1.6: https://jsfiddle.net/14dtfh51/9/

Seems an issue with normalize children. I'll try to make a patch.

I'm still seeing a similar problem when running against the latest code.

Example: https://dankuck.github.io/TiltMaker/buggy.html

References: https://cdn.rawgit.com/vuejs/vue/dev/dist/vue.js

Github: https://github.com/dankuck/TiltMaker

So, what's going on here.. Any updates?

if there's a bug, please, open a new issue with the corresponding repro

Any updates regarding this? I am getting the same error. My code is very similar to the first post.

As many will stumble upon this issue:

The error introduced in vue@2.5.0 is similar to the one reported in this issue, but in fact it is a regression that has already been fixed in vue@2.5.1. Just update to the latest patch release, which is vue@2.5.2 at the moment.

Issue: #6790

Commit: 1f84dd1

Release: https://github.com/vuejs/vue/releases/tag/v2.5.2

I finally solved my problem when I realized that I was loading a separate version of Vue on the page. Only the one webpacked into my distribution files was necessary.