题 :
    如果我们要从query中提取数据的话，可以使用 URLSearchParams ，非常方便。
    你能否自己实现一个和URLSearchParams基本一样的MyURLSearchParams？

    const params = new MyURLSearchParams(‘?a=1&a=2&b=2’)
    params.get(‘a’) // ‘1’
    params.getAll(‘a’) // [‘1’, ‘2’]
    params.get(‘b’) // ‘2’
    params.getAll(‘b’) // [‘2’]

    params.append(‘a’, 3)
    params.set(‘b’, ‘3’)
    params.toString() // ‘a=1&a=2&b=3&a=3’

    1. class MyURLSearchParams {
    2.   /**
    3.    * @params {string} init
    4.    */
    5.   constructor(init) {
    6.     this.params = init
    7.       .replace(/^\?/, '')
    8.       .split('&')
    9.       .map((param) => param.split('='))
    10.   }
    12.   /**
    13.    * @params {string} name
    14.    * @params {any} value
    15.    */
    16.   append(name, value) {
    17.     this.params.push([name, String(value)])
    18.   }
    20.   /**
    21.    * @params {string} name
    22.    */
    23.   delete(name) {
    24.     this.params = this.params.filter((param) => param[0] !== name)
    25.   }
    27.   /**
    28.    * @returns {Iterator}
    29.    */
    30.   *entries() {
    31.     for (let i = 0; i < this.params.length; i++) {
    32.       yield [this.params[i][0], this.params[i][1]]
    33.     }
    34.   }
    36.   /**
    37.    * @param {(value, key) => void} callback
    38.    */
    39.   forEach(callback) {
    40.     this.params.forEach(param => {
    41.       callback.apply(this, [param[1], param[0]])
    42.     })
    43.   }
    45.   /**
    46.    * @param {string} name
    47.    * returns the first value of the name
    48.    */
    49.   get(name) {
    50.     return this.params.find((param) => param[0] === name)?.[1] || null
    51.   }
    53.   /**
    54.    * @param {string} name
    55.    * @return {string[]}
    56.    * returns the value list of the name
    57.    */
    58.   getAll(name) {
    59.     return this.params
    60.       .filter((param) => param[0] === name)
    61.       .map((param) => param[1])
    62.   }
    64.   /**
    65.    * @params {string} name
    66.    * @return {boolean}
    67.    */
    68.   has(name) {
    69.     return this.params.some((param) => param[0] === name)
    70.   }
    72.   /**
    73.    * @return {Iterator}
    74.    */
    75.   keys() {
    76.     return this.params.map((param) => param[0])
    77.   }
    79.   /**
    80.    * @param {string} name
    81.    * @param {any} value
    82.    */
    83.   set(name, value) {
    84.     const exists = this.params.some((param) => {
    85.       if (param[0] !== name) return false
    87.       param[1] = String(value)
    88.       return true
    89.     })
    91.     if (!exists) {
    92.       this.append(name, value)
    93.     }
    94.   }
    96.   // sort all key/value pairs based on the keys
    97.   sort() {
    98.     this.params.sort((a, b) => {
    99.       if (a[0] > b[0]) return 1
    100.       if (a[0] < b[0]) return -1
    101.       return 0
    102.     })
    103.   }
    105.   /**
    106.    * @return {string}
    107.    */
    108.   toString() {
    109.     return this.params.map((param) => param.join('=')).join('&')
    110.   }
    112.   /**
    113.    * @return {Iterator} values
    114.    */
    115.   values() {
    116.     return this.params.map((param) => param[1])
    117.   }
    118. }

    *entries() {} 这个怎么弄? 还不太明白;

    MyURLSearchParams('?a=1&b=2')  

'a=1&b=2' is also acceptable  

MyURLSearchParams doesn't parse full url 'https://google.com?a=1&b=2'  

append() should work for string  

append() should store string values if non-string is passed  

delete() should work,'?a=1&a=1&b=2'  

entries() should work, 'a=1&a=1&a=2&b=2'   

forEach() should work, 'a=1&a=1&a=2&b=2'   

get() should work, 'a=2&a=1&a=2&b=2'   

getAll() should work, 'a=2&a=1&a=2&b=2'   

has() should work, 'a=2&a=1&a=2&b=2'   

keys() should work, 'a=2&a=1&a=2&b=2'   

set() should work, 'a=2&a=1&a=2&b=2'   

sort() should work, 'c=2&a=2&a=1&a=2&b=2'   

toString() should work, '?c=2&a=2&a=1&a=2&b=2'   

values() should work, '?c=2&a=2&a=1&a=2&b=2'