Dynamically insert child components inside vuejs2 data (without $compile or abusing v-html)

Question

I'd like to insert new vuejs components on the fly, at arbitrary points within a block of not-necessarily-predefined HTML.

Here's a slightly contrived example that demonstrates the sort of thing I'm trying to do:

Vue.component('child', {
  // pretend I do something useful
  template: '<span>--&gt;<slot></slot>&lt;--</span>'
})

Vue.component('parent', {
  data() {
    return {
      input: 'lorem',
      text: '<p>Lorem ipsum dolor sit amet.</p><p><i>Lorem ipsum!</i></p>'
    }
  },
  template: `<div>
      Search: <input type='text' v-model="input"><br>
      <hr>
      This inserts the child component but doesn't render it 
      or the HTML:
      <div>{{output}}</div>
      <hr>
      This renders the HTML but of course strips out the child component:
      <div v-html="output"></div>
      <hr>
      (This is the child component, just to show that it's usable here: 
      <child>hello</child>)
      <hr>
      This is the goal: it renders both the input html 
      and the inserted child components:
      TODO ¯\_(ツ)_/¯
    </div>`,
  computed: {
    output() {
      /* This is the wrong approach; what do I replace it with? */
      var out = this.text;
      if (this.input) {
        this.input = this.input.replace(/[^a-zA-Z\s]/g,'');
        var regex = new RegExp(this.input, "gi");
        out = out.replace(regex, '<child><b>' + this.input + '</b></child>');
      }
      return out;
    }
  }
});

new Vue({
  el: '#app'
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.3.0/vue.js"></script>
<div id="app">
  <parent></parent>
</div>

In the above snippet, assume data.text is sanitized HTML. <child> is some sub-component that does something useful, which I want to wrap around chunks of data.text that aren't known ahead of time. (input is just for demo here. This MCVE doesn't really resemble the code I'm building, it's just an example that shows the sort of situation I'm stuck on.)

So: how would I change either the output function or the parent component's template, such that both the HTML from input and the inserted <child> templates are rendered properly?

What I've tried

• In Vue 1, the answer to this would be a straightforward $compile. I'm using vuejs2 which removed $compile (out of justifiable concern that it made it too easy to naively introduce XSS vulnerabilities.)

• v-html sanitizes what you feed it, which strips the child component out. Obviously this is not the way to do this. (That page suggests using partials instead, but I'm not sure how that could be applied to this situation; in any case partials have also been removed from vue2.)

• I've tried passing the results of output() into another component which would then use it as its template. This seems like a promising approach, but I can't figure out how to change that secondary component's template. template only accepts a string, not a function like many of the other component properties, so I can't pass the template html in, say, a prop. Something like rewriting this.template inside beforeMount() or bind() would have been nice, but no joy there either. Is there some other way to replace a component's template string before it's mounted?

• Unlike template, I can pass data to a component's render() function... but then I'm still stuck having to parse that html string into nested createElement functions. Which is exactly what Vue is doing internally in the first place; is there some way to hook into that here short of reinventing it myself?

Vue.component('foo', {
  props: ['myInput'],
  render(createElement) {
    console.log(this.myInput); // this works...
    // ...but how to parse the html in this.myInput into a usable render function?
    // return createElement('div', this.myInput);
  },
})

• I wasn't able to cheat my around this with inline-template, either: <foo inline-template>{{$parent.output}}</foo> does exactly the same thing as a plain old {{output}}. In retrospect that should have been obvious, but it was worth a shot.

• Maybe constructing an async component on the fly is the answer? This could clearly generate a component with an arbitrary template, but how would I reasonably call that from the parent component, and feed output to the constructor? (It would need to be reusable with different input, with multiple instances potentially visible simultaneously; no globals or singletons.)

• I've even considered ridiculous stuff like having output() split the input into an array at the points where it would have inserted <child>, and then doing something like this in the main template:

  ...
  <template v-for="chunk in output">
      <span v-html="chunk"></span>
      <child>...</child>
  </template>
  ....

That would be doable, if laborious -- I'd have to split out what goes in the child's slot into a separate array too and get it by index during the v-for, but that could be done... if input were plain text instead of HTML. In splitting HTML I'll often wind up with unbalanced tags in each chunk, which can mess up the formatting when v-html rebalances it for me. And anyway this whole strategy feels like a bad hack; there must be a better way.

• Maybe I just drop the whole input into a v-html and then (somehow) insert the child components at the proper positions through after-the-fact DOM manipulation? I haven't explored this option too deeply because it, too, feels like a hack, and the reverse of the data-driven strategy, but maybe it's a way to go if all else fails?

A couple of pre-emptive disclaimers

• I'm very well aware of the XSS risks involved in $compile-like operations. Please be assured that none of what I'm doing involves unsanitized user input in any way; the user isn't inserting arbitrary component code, instead a component needs to insert child components at user-defined positions.
• I'm reasonably confident that this is not an XY problem, that I really do need to insert components on the fly. (I hope it's obvious from the number of failed attempts and blind alleys I've run down that I've put more than a little thought into this one!) That said, if there's a different approach that leads to similar results, I'm all ears. The salient point is that I know which component I need to add, but I can't know ahead of time where to add it; that decision happens at run time.
• If it's relevant, in real life I'm using the single-file component structure from vue-cli webpack template, not Vue.component() as in the samples above. Answers that don't stray too far from that structure are preferred, though anything that works will work.

Progress!

@BertEvans points out in comments that Vue.compile() is a thing that exists, which is an I-can't-believe-I-missed-that if ever there was one.

But I'm still having trouble using it without resorting to global variables as in that documentation. This renders, but hardcodes the template in a global:

var precompiled = Vue.compile('<span><child>test</child></span>');
Vue.component('test', {
  render: precompiled.render,
  staticRenderFns: precompiled.staticRenderFns
});

But various attempts to rejigger that into something that can accept an input property have been unsuccessful (the following for example throws "Error in render function: ReferenceError: _c is not defined", I assume because the staticRenderFns aren't ready to go when render needs them?

Vue.component('test', {
  props: ['input'],
  render() { return Vue.compile(this.input).render()},
  staticRenderFns() {return Vue.compile(this.input).staticRenderFns()}
});

(It's not because there are two separate compile()s -- doing the precompile inside beforeMount() and then returning its render and staticRenderFns throws the same error.)

This really feels like it's on the right track but I'm just stuck on a dumb syntax error or the like...

Answer 1

As mentioned in the my comment above, $compile was removed, but Vue.compile is available in certain builds. Using that below works as I believe you intend except in a couple cases.

Vue.component('child', {
  // pretend I do something useful
  template: '<span>--&gt;<slot></slot>&lt;--</span>'
})

Vue.component('parent', {
  data() {
    return {
      input: 'lorem',
      text: '<div><p>Lorem ipsum dolor sit amet.</p><p><i>Lorem ipsum!</i></p></div>'
    }
  },
  template: `<div>
      Search: <input type='text' v-model="input"><br>
      <hr>
      <div><component :is="output"></component></div>
    </div>`,
  computed: {
    output() {
      if (!this.input)
         return Vue.compile(this.text)
      /* This is the wrong approach; what do I replace it with? */
      var out = this.text;
      if (this.input) {
        this.input = this.input.replace(/[^a-zA-Z\s]/g,'');
        var regex = new RegExp(this.input, "gi");
        out = out.replace(regex, '<child><b>' + this.input + '</b></child>');
        out = Vue.compile(out)
      }
      return out;
    }
  }
});

new Vue({
  el: '#app'
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.3.0/vue.js"></script>
<div id="app">
  <parent></parent>
</div>

You mentioned you are building with webpack and I believe the default for that build is Vue without the compiler, so you would need to modify it to use a different build.

I added a dynamic component to accept the results of the compiled output.

The sample text is not a valid template because it has more than one root. I added a wrapping div to make it a valid template.

One note: this will fail if the search term matches all or part of any of the HTML tags in the text. For example, if you enter "i", or "di" or "p" the results will not be what you expect and certain combinations will throw an error on compilation.

Answer 2

I'm posting this as a supplement to Bert Evans's answer, for the benefit of vue-cli webpack users who want to use .vue files instead of Vue.component(). (Which is to say, I'm mostly posting this so I'll be able to find this information when I inevitably forget it...)

Getting the right Vue build

In vue-cli 2 (and possibly 1?), to ensure Vue.compile will be available in the distribution build, confirm webpack.base.conf.js contains this line:

'vue$': 'vue/dist/vue.esm.js' // or vue/dist/vue.common.js for webpack1

instead of 'vue/dist/vue.runtime.esm.js'. (If you accepted the defaults when running vue init webpack you will already have the full standalone build. The "webpack-simple" template also sets the full standalone build.)

Vue-cli 3 works somewhat differently, and does not have Vue.compile available by default; here you'll need to add the runtimeCompiler rule to vue.config.js:

module.exports = {
    /* (other config here) */
    runtimeCompiler: true
};

The component

The "child" component can be a normal .vue file, nothing special about that.

A bare-bones version of the "parent" component would be:

<template>
    <component :is="output"></component>
</template>
<script>
import Vue from 'vue';
import Child from './Child'; // normal .vue component import

export default {
  name: 'Parent',
  computed: {
    output() {
      var input = "<span>Arbitrary single-root HTML string that depends on <child></child>.  This can come from anywhere; don't use unsanitized user input though...</span>";
      var ret = Vue.compile(input);
      ret.components = { Child };  // add any other necessary properties similarly
      ret.methods = { /* ... */ }  // like so
      return ret;
    }
  }
};
</script>

(The only significant difference between this and the non-webpack version is importing the child, then declaring the component dependencies as ret.components: {Child} before returning it.)