javascript meteor meteor-blaze spacebars html-templates

Meteor Blaze access Template.contentBlock inside Template.onCreated

I am writing a custom Blaze block helper with children:

<template name="parent">
    {{> Template.contentBlock ..}}
</template>

<template name="child">
    {{> Template.contentBlock ..}}
</template>

My intended use case would be to have a Template with arbitrary child nodes, that I define in the html file.

{{#parent}}

  {{#child id="child1" title="Child 1"}}
    <p>This is content of child 1</p>
  {{/child}}

  {{#child id="child2" title="Child 2"}}
    <p>This is content of child 2</p>
  {{/child}}

  {{#child id="childN" title="Child N"}}
    <p>This is content of child N</p>
  {{/child}}

{{/parent}}

No problem so far. However, in the parent Template's onCreated / autorun I want to have access to child templates. I want to use this data to dynamically create in the parent Template elements, based

Template.parent.onCreated(function () {
    const instance = this;
    instance.state = new ReactiveDict();

    instance.autorun(function () {
        const contentBlocks = // how?
        instance.state.set("children", contentBlocks);
    });
});

Template.parent.helpers({
    children() {
        return Template.instance().state.get("children");
    }
});

Where children would be used in the parent template as following:

{{#parent}}

  {{#each children}}
    do something with {{this.value}}
  {{/each}}      

  {{#child id="child1" title="Child 1"}}
    <p>This is content of child 1</p>
  {{/child}}

  {{#child id="child2" title="Child 2"}}
    <p>This is content of child 2</p>
  {{/child}}

  {{#child id="childN" title="Child N"}}
    <p>This is content of child N</p>
  {{/child}}

{{/parent}}

What I don't want is to access the contentBlock's content (the <p>) but rather get a list of the added child Templates.

Is that possible with the current Template / Blaze API? The documentation is a bit thin on that point.

It is basically the opposite of this post: How to get the parent template instance (of the current template)

Edit 1: Use parent View's Renderfunction (only partially working)

I found a way to get the parent Template's children but not their data reactively:

// in Template.parant.onCreated -> autorun
const children = instance.view.templateContentBlock.renderFunction()
    .filter(child => typeof child === 'object')
    .map(el => Blaze.getData(el._render()));
console.log(children);
// null, null, null because Blaze.getData(view) does return null

Another approach I found is to used a shared ReactiveVar but both seem to me not clean enough. I just want to get the list of Template instances in the parent's js code.

Edit 2: Use a shared ReactiveVar (only partially working)

It is possible to use a shared ReactiveVar as long as it is in the scope of both Templates:

const _cache = new ReactiveVar({});

Template.parent.onCreated(function () {
    const instance = this;
    instance.state = new ReactiveDict();

    instance.autorun(function () {
        const children = Object.values(_cache.get());
        instance.state.set("children", children);
    });
});

Template.parent.helpers({
    children() {
        return Template.instance().state.get("children");
    }
});

Working (but only rendered once, not reactive):

Template.child.onCreated(function () {
    const instance = this;
    const data = Template.currentData();
    const cache = _cache.get();
    cache[data.id] = data;
    _cache.set(cache);
});

Not working (child autorun is setting values, but new values are not rendered):

Template.child.onCreated(function () {
    const instance = this;
    instance.autorun(function() {
        const instance = this;
        const data = Template.currentData();
        const cache = _cache.get();
        cache[data.id] = data;
        _cache.set(cache);
    });
});

Solution

here is what I came up with. Pls let me know if that is what you wanted or if I misunderstood.

main.html:

<body>
    {{> content}}
</body>

<template name="content">
    {{#parent}}

        {{#each children}}
            <p>do something with {{this.id}}</p>
            <p>data: {{this.tmpl.data.title}}</p>
        {{/each}}

        {{#child id="child1" title="Child 1" parentTemplate=this.parentTemplate}}
            <p>This is content of child 1</p>
        {{/child}}

        {{#child id="child2" title="Child 2" parentTemplate=this.parentTemplate }}
            <p>This is content of child 2</p>
        {{/child}}

        {{#child id="childN" title="Child N" parentTemplate=this.parentTemplate }}
            <p>This is content of child N</p>
        {{/child}}

    {{/parent}}
</template>

<template name="parent">
    {{> Template.contentBlock parentTemplate=template}}
</template>

<template name="child">
    {{> Template.contentBlock }}
</template>

main.js

import { Template } from 'meteor/templating';
import { ReactiveVar } from 'meteor/reactive-var';

import './main.html';

Template.content.helpers({
    children() {
        return this.parentTemplate.children.get();
    },
});

Template.parent.onCreated(function () {
    this.children = new ReactiveVar([]);
});

Template.parent.helpers({
    template() {
        return Template.instance();
    }
});

Template.child.onRendered(function () {
    const children = this.data.parentTemplate.children.get();
    children.push({ id: this.data.id, tmpl: this });
    this.data.parentTemplate.children.set(children);
});

Output:

Although it uses ReactiveVar which is not ideal it does not rely on any global and you can put your code in different files, no problem.