Best way to convert an accept type object to equv. string

gistfile1.txt

Best way to convert acceptType object to a string like below?

From:
var acceptTypes = {
  'Images': ['*.png','*.jpg'],
  'Documents': ['*.docx']
}

To:
var acceptType = 'Images:*.png,*.jpg;Documents:*.docx'

var out = Object.keys(acceptTypes).reduce(function(acc, key) {
  var val = acceptTypes[key]
  acc.push(key + ':' + val.join(','));
  return acc;
}, []).join(';')

@polotek lol i came up with the exact same solution (with the 2 semicolons you're missing, of course)