实现 JSON parse / stringify

[fedono]

/**
 * @param {string} str
 * @return {object | Array | string | number | boolean | null}
 */
function parse(str) {
  if(str === '') {
    throw Error();
  }
  if(str[0] === "'") {
    throw Error();
  }
  if(str === 'null') {
    return null;
  }
  if(str === '{}') {
    return {};
  }
  if(str === '[]') {
    return [];
  }
  if(str === 'true') {
    return true;
  }
  if(str === 'false') {
    return false;
  }
  if(str[0] === '"') {
    return str.slice(1, -1);
  }
  if(+str === +str) {
    return Number(str);
  }
  if(str[0] === '{') {
    return str.slice(1, -1).split(',').reduce((acc, item) => {
      const index = item.indexOf(':');
      const key = item.slice(0, index)
      const value = item.slice(index + 1);
      acc[parse(key)] = parse(value);
      return acc;
    }, {});
  }
  if(str[0] === '[') {
    return str.slice(1, -1).split(',').map((value) => parse(value));
  }
}

来源 - implement-JSON-parse

[fedono]

取巧的方案

/**
 * @param {string} str
 * @return {object | Array | string | number | boolean | null}
 */
function parse(str) {
    let result = (new Function(`return ${str.replace(/\"/g,"'")}`))();

    if(str !== JSON.stringify(result)) {
      throw new Error("Nope");
    }

    return result;
}

[fedono]

实现 stringify

/**
 * @param {any} data
 * @return {string}
 */
function stringify(data) {
  if(typeof data === 'bigint') {
    throw new Error('Do not know how to serialize a BigInt at JSON.stringify');
  } 
  if(typeof data === 'string') {
    return `"${data}"`;
  } 
  if(typeof data === 'function') {
    return undefined;
  }
  if(data !== data) {
    return 'null';
  }
  if(data === Infinity) {
    return 'null';
  }
  if(data === -Infinity) {
    return 'null';
  }
  if(typeof data === 'number') {
   return `${data}`;
  }
  if(typeof data === 'boolean') {
    return `${data}`;
  }
  if(data === null) {
    return 'null';
  }
  if(data === undefined) {
    return 'null';
  }
  if(typeof data === 'symbol') {
    return 'null';
  }
  if(data instanceof Date) {
    return `"${data.toISOString()}"`;
  }
  if(Array.isArray(data)) {
    const arr = data.map((el) => stringify(el));
    return `[${arr.join(',')}]`;
  }
  if(typeof data === 'object') {
    const arr = Object.entries(data).reduce((acc, [key, value]) => {
      if(value === undefined) {
        return acc;
      }
      acc.push(`"${key}":${stringify(value)}`);
      return acc;
    }, [])
    return `{${arr.join(',')}}`;
  }
}

来源 - implement-JSON-stringify