gistfile1.js

var textEl = document.createElement('div'),
  container = document.createElement('div'),
  lineHeight = 25 // pixels of a single line
container.appendChild(textEl)
function showText(text) {
  // hide the text while we test its layout. visibility='hidden' still keeps the element in the DOM, in contrast to display='none'
  textEl.style.visibility = 'hidden'
  textEl.innerHTML = text
  textEl.style.textAlign = (textEl.offsetHeight > lineHeight
    ? 'left' // overflowing onto two lines
    : 'center') // fits on a single line
  textEl.style.visibility = 'visible'
}