Function codePointAt

packages/breaker/src/index.ts:33–55

(str: string, idx: number)

const classTrie = new UnicodeTrie(data);

const codePointAt = (str: string, idx: number) => {
  // different from String#codePointAt with low surrogate
  const code = str.charCodeAt(idx);
  // High surrogate
  if (0xd800 <= code && code <= 0xdbff) {
    const hi = code;
    const low = str.charCodeAt(idx + 1);
    if (0xdc00 <= low && low <= 0xdfff) {
      return (hi - 0xd800) * 0x400 + (low - 0xdc00) + 0x10000;
    }
    return hi;
  }
  // Low surrogate
  if (0xdc00 <= code && code <= 0xdfff) {
    const hi = str.charCodeAt(idx - 1);
    const low = code;
    if (0xd800 <= hi && hi <= 0xdbff) {
      return (hi - 0xd800) * 0x400 + (low - 0xdc00) + 0x10000;
    }
    return low;
  }
  return code;
};

const isSurrogate = (str: string, pos: number) => {
  let ref, ref1;