/** * @param {string} str * @return {object | Array | string | number | boolean | null} */const emptyMap = {  'n': '\n',  'b': '\b',  't': '\t',  '\\': '\\',  '\'': '\'', }function parse(str) {  let index = 0;  function _parse() {    skipWhiteSpaces();    let char = str[index];    if(char === "t")return parseValue("true", true);    if(char === "f")return parseValue("false", false);    if(char === "n")return parseValue("null", null);    if(char === '"')return parseString();    if(char === '[')return parseArray();    if(char === '{')return parseObject();    if(isDigit(char) || char === '+' || char === '-')return parseNumber();    throw new Error('invalid json character');      }  function parseValue(value, returnValue) {    if(str.substring(index, value.length + index) === value){      index += value.length;      return returnValue;    }    else {      throw new Error('invalid boolean json character');    }  }  function parseNumber() {    let start = index;    if(str[index] === '+' || str[index] === '-' || str[index] === '0')index++;    while(index < str.length && isDigit(str[index])) {      index++;    }        if(str[index] === '.') {      index++;      while(index < str.length && isDigit(str[index])) {        index++;      }    }    return Number(str.substring(start, index));  }  function parseString() {    let s = "";    index++;    while(index < str.length) {      let char = str[index];      if(char === '"'){        index++;        return s;      }      if(char === "\\") {        index++;        let escapeChar = str[index];        s += emptyMap[escapeChar] ?? escapeChar;      }      else s += char;      index++;    }  }  function parseArray() {    index++;    skipWhiteSpaces();    let arr = [];//[1,2,3]    if(str[index] === ']')return arr;    while(index < str.length) {      let val = _parse();      arr.push(val);      const char = str[index];      if(char === ',') {        index++;        skipWhiteSpaces();      } else if(char === ']') {        index++;        return arr;      } else {        throw new Error('Array should end with ]')      }    }  }  function parseObject() {    index++;    skipWhiteSpaces();    let obj = {}; //{"key": "value",    "key2":   "value2", }, {}    if(str[index] === '}') {      index++;      return obj;    }    while(index < str.length) {      const char = str[index];      if(char !== '"')throw new Error('object key should be string');      const key = parseString();      skipWhiteSpaces();      if(str[index] !== ':')throw new Error('object should have semi-colon');      index++;      const value = _parse();      obj[key] = value;      skipWhiteSpaces();      if(str[index] === ','){        index++;        skipWhiteSpaces();      }      else if(str[index] === '}') {        index++;        return obj;      } else {        throw new Error('invalid json object character');      }    }  }  let res = _parse(str);  if(index < str.length) {    throw new Error('invalid json character');  }  return res;  function skipWhiteSpaces() {    while(index < str.length && /\s/.test(str[index]))index++;  }  function isDigit(ch) {    return ch <= '9' && ch >= '0';  }}//"123"//"true"//'"hello"'//'[1,2,3,"4"]'//'{"key":"value"}'console.log(parse('[{"a":{"b":{"c":[1]}}},null,"str"]' ))