No-lib json tokenizer

json-tokenizer.js

const t = {
  token: (value) => ({ type: 'token', value }),
  literal: (value) => ({ type: 'literal', value }),
};
const escapes = {
  '"': '"',
  '\\': '\\',
  b: '\b',
  f: '\f',
  n: '\n',
  r: '\r',
  t: '\t',
};

export function* tokenize (input) {
  let state = 'base';
  let escaped = false;
  let literal = '';

  for (const char of input) {
    if (state === 'base') {
      if (char === '"') {
        state = 'string';
      } else if ('{}[]:,'.includes(char)) {
        yield t.token(char);
      } else {
        throw new SyntaxError();
      }
    } else if (state === 'string') {
      if (escaped) {
        if (escapes.hasOwnProperty(char)) {
          literal += escapes[char];
        } else if (char === 'u') {
          // TODO handle unicode escapes : (
        } else {
          literal += char;
        }
        escaped = false;
      } else if (char === '\\') {
        escaped = true;
      } else if (char === '"') {
        yield t.literal(literal);
        literal = '';
        state = 'base';
      } else {
        literal += char;
      }
    }
  }
}