JavaScript 手写

JSON.stringify

功能点

1. symbol function undefined 返回 undefined
2. bigInt 报错
3. NaN, Infinity, null 返回 'null'
4. 存在 toJSON 直接使用
5. boolean 和 number 直接转 string
6. symbol 键忽略

辅助函数

1. 处理循环对象 isCyclic
2. 获取对象类型 getType

const jsonstringify = (data) => {
  // Check if an object has a circular reference
  const isCyclic = (obj) => {
    // Use a Set to store the detected objects
    let stackSet = new Set()
    let detected = false

    const detect = (obj) => {
      // If it is not an object, we can skip it directly
      if (obj && typeof obj != 'object') {
        return
      }
      // When the object to be checked already exists in the stackSet,
      // it means that there is a circular reference
      if (stackSet.has(obj)) {
        return (detected = true)
      }
      // save current obj to stackSet
      stackSet.add(obj)

      for (let key in obj) {
        // check all property of `obj`
        if (obj.hasOwnProperty(key)) {
          detect(obj[key])
        }
      }
      // After the detection of the same level is completed,
      // the current object should be deleted to prevent misjudgment
      /*
        For example: different properties of an object may point to the same reference,
        which will be considered a circular reference if not deleted

        let tempObj = {
          name: 'bytefish'
        }
        let obj4 = {
          obj1: tempObj,
          obj2: tempObj
        }
      */
      stackSet.delete(obj)
    }

    detect(obj)

    return detected
  }

  // Throws a TypeError ("cyclic object value") exception when a circular reference is found.
  if (isCyclic(data)) {
    throw new TypeError('Converting circular structure to JSON')
  }

  // Throws a TypeError  when trying to stringify a BigInt value.
  if (typeof data === 'bigint') {
    throw new TypeError('Do not know how to serialize a BigInt')
  }

  const type = typeof data
  const commonKeys1 = ['undefined', 'function', 'symbol']
  const getType = (s) => {
    return Object.prototype.toString
      .call(s)
      .replace(/\[object (.*?)\]/, '$1')
      .toLowerCase()
  }

  if (type !== 'object' || data === null) {
    let result = data
    // The numbers Infinity and NaN, as well as the value null, are all considered null.
    if ([NaN, Infinity, null].includes(data)) {
      result = 'null'

      // undefined, arbitrary functions, and symbol values are converted individually and return undefined
    } else if (commonKeys1.includes(type)) {
      return undefined
    } else if (type === 'string') {
      result = '"' + data + '"'
    }

    return String(result)
  } else if (type === 'object') {
    // If the target object has a toJSON() method, it's responsible to define what data will be serialized.

    // The instances of Date implement the toJSON() function by returning a string (the same as date.toISOString()). Thus, they are treated as strings.
    if (typeof data.toJSON === 'function') {
      return jsonstringify(data.toJSON())
    } else if (Array.isArray(data)) {
      let result = data.map((it) => {
        // 3# undefined, Functions, and Symbols are not valid JSON values. If any such values are encountered during conversion they are either omitted (when found in an object) or changed to null (when found in an array).
        return commonKeys1.includes(typeof it) ? 'null' : jsonstringify(it)
      })

      return `[${result}]`.replace(/'/g, '"')
    } else {
      // 2# Boolean, Number, and String objects are converted to the corresponding primitive values during stringification, in accord with the traditional conversion semantics.
      if (['boolean', 'number'].includes(getType(data))) {
        return String(data)
      } else if (getType(data) === 'string') {
        return '"' + data + '"'
      } else {
        let result = []
        // 7# All the other Object instances (including Map, Set, WeakMap, and WeakSet) will have only their enumerable properties serialized.
        Object.keys(data).forEach((key) => {
          // 4# All Symbol-keyed properties will be completely ignored
          if (typeof key !== 'symbol') {
            const value = data[key]
            // 3# undefined, Functions, and Symbols are not valid JSON values. If any such values are encountered during conversion they are either omitted (when found in an object) or changed to null (when found in an array).
            if (!commonKeys1.includes(typeof value)) {
              result.push(`"${key}":${jsonstringify(value)}`)
            }
          }
        })

        return `{${result}}`.replace(/'/, '"')
      }
    }
  }
}

参考：https://mp.weixin.qq.com/s/LKAZ8J0mlwt5ultYjdmg9w