Component rendered as comment in VueJS + JSPM

import Vue from "vue" will pull in the runtime-only build which does not include the template compiler, this means that you will need to have pre-compiled your templates. If you take your example and use the runtime-only build you should receive the following message:

[Vue warn]: Failed to mount component: template or render function not defined. (found in root instance)

As you can see here: https://jsfiddle.net/aqxL6sjL/

In order to get that to work with the runtime-only build, I would need to create a render function on the Vue instance, like so:

const app = new Vue({
  el: '#app',
  render: function(createElement) {
    return createElement('div', {}, this.message)
  },
  data: {
    message: 'Hello Vue!'
  }
});

Here's the updated fiddle: https://jsfiddle.net/aqxL6sjL/1/

And that is what vueify and vue-loader do when used with browserify and webpack respectively, therefore the template compiler is not needed. If you are using jspm you may want to take a look at: systemjs-plugin-vue, however, it's no longer maintained, so it may no longer work.

I would suggest that the easiest route is to bundle the standalone-build instead of the runtime only build. I don't use jspm, but I guess it would be something like:

 import Vue from 'vue/dist/vue.common.js';

The issue there though is that you may get both the runtime and standalone builds being imported when using third party libraries which will cause errors, so it's recommended to alias them so you get the correct build, however, I cannot say how you would do this is jspm but I would guess that it's the map functionality: https://github.com/jspm/registry/wiki/Configuring-Packages-for-jspm#map-configuration.

I'm never opinionated about a developers choice of tools, but if you are starting a fresh vue project, I would suggest you use webpack or browserify instead, because they have much better support, even down to the point that you can pull in scaffolding directly via the vue-cli. In the long run that may save you quite a lot of hassle in trying to get your projects up and running and asking for help in future.