truncate-util.js

const warning = (maxLength, startLimit, endLimit, delimiter) => (
  console.warn(`middleEllipsis :: The start (${startLimit}) and end \
(${endLimit}) plus the delimiter (${delimiter}) add up to more than \
the limit (${startLimit + endLimit + delimiter.length} > ${maxLength}). \
This will produce a truncated string larger than your maxLength.`)
)

const middleEllipsis = ({ text = '', maxLength = 47, start, end, delimiter = '...' }) => {
  if (text.length < maxLength) { return text }
  const startLimit = start || Math.floor((maxLength - delimiter.length) / 1.6)
  const endLimit = end || Math.floor(maxLength - delimiter.length - startLimit)
  if (start && end && startLimit + endLimit + delimiter.length > maxLength) {
    warning(maxLength, startLimit, endLimit, delimiter)
  }
  return `${text.substring(0, startLimit)}${delimiter}${text.substring(text.length - endLimit, text.length)}`
}

const middleEllipsisTagFactory = ({ maxLength, start, end, delimiter }) => (
  (texts, ...rest) => middleEllipsis({
    text: texts.reduce((str, text, index) => `${str}${text}${rest[index] ? rest[index] : ''}`, ''),
    maxLength, start, end, delimiter
  })
)

const truncateMiddleMax10 = middleEllipsisTagFactory({ maxLength: 10 })

truncateMiddleMax10`This is some long text that must be truncated!`
// output --> 'This...ed!'