Check if textNode has text on multiple lines

getTextLines.js

// console.log(getTextLines(querySelector('span')))
// returns number of lines

function collapseWhiteSpace(value) {
  return value.trim().replace(/\s+/g, ' ')
}

function getTextLines(textNode) {
  if (textNode.nodeType !== 3) {
    return false // Only text nodes allowed
  }

  textNode.textContent = collapseWhiteSpace(textNode.textContent)

  var textContent = textNode.textContent
  var range = document.createRange()
  var lines = []
  var lineCharacters = []

  // Iterate over every character in the text node.
  for (var i = 0; i < textContent.length; i++) {
    // Set the range to span from the beginning of the text node up to and
    // including the current character (offset).
    range.setStart(textNode, 0)
    range.setEnd(textNode, i + 1)

    // At this point, the Range's client rectangles will include a rectangle
    // for each visually-rendered line of text. Which means, the last
    // character in our Range (the current character in our for-loop) will be
    // the last character in the last line of text (in our Range). As such, we
    // can use the current rectangle count to determine the line of text.
    var lineIndex = range.getClientRects().length - 1

    // If this is the first character in this line, create a new buffer for
    // this line.
    if (!lines[lineIndex]) {
      lines.push((lineCharacters = []))
    }

    // Add this character to the currently pending line of text.
    lineCharacters.push(textContent.charAt(i))
  }

  // At this point, we have an array (lines) of arrays (characters). Let's
  // collapse the character buffers down into a single text value.
  lines = lines.map(function operator(characters) {
    return collapseWhiteSpace(characters.join(''))
  })

  return lines.length
}