/**
 * @description: utf8to16
 * @param {String} str
 * @return {String}
 */
export default function utf8to16(str) {
  var out, i, len, c;
  var char2, char3;
  out = '';
  len = str.length;
  i = 0;
  while (i < len) {
    c = str.charCodeAt(i++);
    switch (c >> 4) {
      case 0:
      case 1:
      case 2:
      case 3:
      case 4:
      case 5:
      case 6:
      case 7:
        out += str.charAt(i - 1);
        break;
      case 12:
      case 13:
        char2 = str.charCodeAt(i++);
        out += String.fromCharCode(((c & 0x1f) << 6) | (char2 & 0x3f));
        break;
      case 14:
        char2 = str.charCodeAt(i++);
        char3 = str.charCodeAt(i++);
        out += String.fromCharCode(((c & 0x0f) << 12) | ((char2 & 0x3f) << 6) | ((char3 & 0x3f) << 0));
        break;
    }
  }
  return out;
}