matchHeights.js

const div = document.createElement('div')
const div_w0 = div.cloneNode()
const div_w100 = div.cloneNode()
const div_flex = div.cloneNode()

div_w0.style.marginRight = '-100%'
div_w0.style.visibility = 'hidden'
div_w0.style.width      = '100%'
div_w0.setAttribute('aria-hidden', true)

div_w100.style.width = '100%'

div_flex.style.display  = 'flex'
div_flex.style.position = 'relative'

function matchHeights([...els]){  
  els.forEach(matchHeight)
}

function matchHeight(subject, {}, siblings){
  const container = div_flex.cloneNode()
  
  siblings.forEach(el => {
    const clone   = el.cloneNode(true)
    const wrapper = (
      el === subject
      ? div_w100 : div_w0
    ).cloneNode()
      
    wrapper.appendChild(clone)
    
    container.appendChild(wrapper)
  })
  
  subject.parentNode.replaceChild(container, subject)
}