Generate a responsive image string based on a filename and some widths

responsiveStringGenerator.js

function generateResponsiveString (filename, widths, isFallback) {
  'use strict'
  
  const urlPrefix = 'https://res.cloudinary.com/beardfury/image/upload/c_scale,w_'
  
  let fullString = ''
  
  if (isFallback) {
    return urlPrefix + widths + filename
  }
  
  widths.forEach(function (width) {
    fullString += urlPrefix + width + filename + ' ' + width + 'w, '
  })
  
  // strip the trailing comma and space
  return fullString.substr(0, fullString.length - 2)
}