Description

set_meta updates the content of a meta tag in the document head.

If no tag is found, it is created.

Example

Here's a Nothing Reflex that updates a meta tag:

  def meta
    cable_ready.set_meta(name: "pill-messages", content: "5").broadcast
    morph :nothing
  end

Motivation

I've found a really interesting pattern for building UI functionality that makes extensive use of meta tags.

<span class="badge badge-md bg-danger text-white" data-controller="pill" data-pill-tag-value="messages">4</span>

This is all tied together with a Stimulus controller that observes meta tags:

import { Controller } from 'stimulus'

export default class extends Controller {
  static values = { tag: String }

  initialize () {
    this.metaTag = document.head.querySelector(
      `meta[name=pill-${this.tagValue}]`
    )
    this.element.textContent = this.metaTag.content
    this.observer = new MutationObserver(this.meta)
  }

  connect () {
    this.observer.observe(this.metaTag, {
      attributeFilter: ['content']
    })
  }

  disconnect () {
    this.observer.disconnect()
  }

  meta = mutation => {
    const content = mutation[0].target.content
    if (content && content !== '0') {
      this.element.textContent = mutation[0].target.content
      this.element.classList.remove('d-none')
    } else {
      this.element.textContent = ''
      this.element.classList.add('d-none')
    }
  }
}

Basically, any menu items which can feature a notification "pill" observe a meta tag for changes, and update themselves when the meta tag is updated. If there is no content or the content is 0, the pill is hidden.

This is very similar to using set_dataset_property with the Values API, except that it has two advantages:

• multiple elements can pick up changes from the meta tag, and they don't have to be aware of each other
• this solution is decoupled from knowing the location of an element in the DOM to receive the dataset property update