function test(str) {
  var _map = {},
      _arr = [],
      entries = str.split(','),
      entry = null,
      entryKV = null,
      entryK = null,
      entryV = null
  for(var i = 0, len = entries.length; i < len; i ++) {
      entry = entries[i]
      entryKV = entry.split(':')
      entryK = 'k' + entryKV[0]
      entryV = 'v' + entryKV[1]
      if (!_map[entryK] && !_map[entryV]) {
          _arr.push(entry)
      }
      _map[entryK] = true
      _map[entryV] = true
  }
  console.log(_arr.join(','))
}
test('4:1,2:3,3:5,4:3')
test('4:1,2:3,5:3,4:2')
test('4:1,2:4,3:5,4:3')


输出

4:1,2:3,3:5
4:1,2:3
4:1,2:4,3:5