New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember - Workaround to yield multiple blocks'
});

templates.application.hbs

<h1>Ember - Workaround to yield multiple blocks</h1>


The <a href="https://github.com/emberjs/rfcs/blob/master/text/0226-named-blocks.md">Named Templates Block API</a> will add the ability to pass multiple blocks to a component.

<br><br>

Meanwhile, a possible workaround could be to split your component into multiple subcomponents and allow to set the subcomponent block by passing them as block parameters. 

<br><br>
{{my-component}}
<br><br>
{{#my-component as |f|}}
  {{f.header}}
  {{#f.content}}
  	Custom content
  {{/f.content}}
  {{f.footer}}
{{/my-component}}
<br><br>

{{#my-component as |f|}}
  {{#f.header}}
     Custom header
  {{/f.header}}
  {{#f.content}}
     Custom content
  {{/f.content}}
  {{#f.footer}}
     Custom footer
  {{/f.footer}}
{{/my-component}}

templates.components.my-component.hbs

<div class="container">
  {{yield (hash
        header = (component 'my-header')
        content = (component 'my-content')
        footer = (component 'my-footer')
   )}}
	{{#unless hasBlock}}
     {{my-header}}
     {{my-content}}
     {{my-footer}}    
	{{/unless}}
</div>

templates.components.my-content.hbs

{{#if hasBlock}}
  {{yield}}
{{else}}
  Default content
{{/if}}

templates.components.my-footer.hbs

{{#if hasBlock}}
  {{yield}}
{{else}}
  Default footer
{{/if}}

templates.components.my-header.hbs

{{#if hasBlock}}
  {{yield}}
{{else}}
  Default header
{{/if}}

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0"
  }
}