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数组 ​

删除一个 ​

js
function removeitem(arr, item) {
  let newstr = str.replace(new RegExp(item, `g`), ``)
  console.log(arr)
  return [...newstr]
}
console.log(removeitem([1, 2, 3, 4, 2], 2))
function removeitem(arr, item) {
  let newstr = str.replace(new RegExp(item, `g`), ``)
  console.log(arr)
  return [...newstr]
}
console.log(removeitem([1, 2, 3, 4, 2], 2))
ts
// 0.0.2/arrayUniqueFilter.js
const arr = [1, 2, 11, 22, 11, 1, 11, 22, 1, 2]
const unique = (arr) =>
  arr.filter(
    (element, index, self) =>
      // Self.indexOf(element) 每次都从数组第一个元素开始往下查
      self.indexOf(element) === index,
  )
console.log(unique(arr)) // [1, 2, 11, 22]

// 上面可简写为
const unique2 = (arr) =>
  arr.filter((element, index, self) => self.indexOf(element) === index)
console.log(unique2(arr)) // [1, 2, 11, 22]

// 元素非对象
const arr3 = [
  { id: 1, name: `张三` },
  { id: 2, name: `李四` },
  { id: 11, name: `王五` },
  { id: 1, name: `张三` },
  { id: 11, name: `王五` },
  { id: 3, name: `李四` },
]
const unique3 = (arr, id) => {
  const cache = []
  for (const item of arr) {
    if (cache.find((v) => v[id] === item[id])) {
      continue
    }
    cache.push(item)
  }
  return cache
}
console.log(unique3(arr3, `id`)) // [{id: 1, name: "张三"}, {id: 2, name: "李四"}, {id: 11, name: "王五"}, {id: 3, name: "李四"}]
export {}
// 0.0.2/arrayUniqueFilter.js
const arr = [1, 2, 11, 22, 11, 1, 11, 22, 1, 2]
const unique = (arr) =>
  arr.filter(
    (element, index, self) =>
      // Self.indexOf(element) 每次都从数组第一个元素开始往下查
      self.indexOf(element) === index,
  )
console.log(unique(arr)) // [1, 2, 11, 22]

// 上面可简写为
const unique2 = (arr) =>
  arr.filter((element, index, self) => self.indexOf(element) === index)
console.log(unique2(arr)) // [1, 2, 11, 22]

// 元素非对象
const arr3 = [
  { id: 1, name: `张三` },
  { id: 2, name: `李四` },
  { id: 11, name: `王五` },
  { id: 1, name: `张三` },
  { id: 11, name: `王五` },
  { id: 3, name: `李四` },
]
const unique3 = (arr, id) => {
  const cache = []
  for (const item of arr) {
    if (cache.find((v) => v[id] === item[id])) {
      continue
    }
    cache.push(item)
  }
  return cache
}
console.log(unique3(arr3, `id`)) // [{id: 1, name: "张三"}, {id: 2, name: "李四"}, {id: 11, name: "王五"}, {id: 3, name: "李四"}]
export {}
ts
// 0.0.2/array_algorithms.js
const arr1 = [1, 7, 4, 5, 2, 1, 5, 3, 6, 2, 1, 3]
const arr2 = [2, 4, 3, 4, 5, 5, 5]

const intersection = (arr1, arr2) => {
  const map = new Map()
  const arr = []
  // 键值对，键是 value，值是 value 出现次数, 出现次数累加
  for (let i = 0; i < arr1.length; i++) {
    const value = arr1[i]
    console.log(map)
    console.log(value)
    let valueInMap = map.get(value)
    console.log(valueInMap)
    valueInMap = (valueInMap ? valueInMap : 0) + 1
    console.log(valueInMap)
    map.set(value, valueInMap)
    console.log(map)
  }
  // 键值对，中转 map 判断第二个数组的值是否存在，存在就留下来，然后 map 值次数减1
  for (let i = 0; i < arr2.length; i++) {
    const value = arr2[i]
    if (map.has(value) && map.get(value) !== 0) {
      arr.push(value)
      map.set(value, map.get(value) - 1)
    }
  }
  return arr
}

console.log(intersection(arr1, arr2)) // [ 2, 4, 3, 5, 5 ]
// 0.0.2/array_algorithms.js
const arr1 = [1, 7, 4, 5, 2, 1, 5, 3, 6, 2, 1, 3]
const arr2 = [2, 4, 3, 4, 5, 5, 5]

const intersection = (arr1, arr2) => {
  const map = new Map()
  const arr = []
  // 键值对，键是 value，值是 value 出现次数, 出现次数累加
  for (let i = 0; i < arr1.length; i++) {
    const value = arr1[i]
    console.log(map)
    console.log(value)
    let valueInMap = map.get(value)
    console.log(valueInMap)
    valueInMap = (valueInMap ? valueInMap : 0) + 1
    console.log(valueInMap)
    map.set(value, valueInMap)
    console.log(map)
  }
  // 键值对，中转 map 判断第二个数组的值是否存在，存在就留下来，然后 map 值次数减1
  for (let i = 0; i < arr2.length; i++) {
    const value = arr2[i]
    if (map.has(value) && map.get(value) !== 0) {
      arr.push(value)
      map.set(value, map.get(value) - 1)
    }
  }
  return arr
}

console.log(intersection(arr1, arr2)) // [ 2, 4, 3, 5, 5 ]
ts
let str = 'abcabcabcbbccccc'
let num = 0
let char = ''
let arr = ['a', 'a', 'b', 'b', 'c', 'c', 'c']
// 使其按照一定的次序排列
let compress = function (chars) {
  chars = chars.join('')
  let temp = []

  let re = /(\w)\1+/g
  chars.replace(re, ($0, $1) => {
    temp.push($1)
    temp.push(String($0.length))
    return temp
  })
  console.log(chars)
  return chars.length
}
console.log(compress(arr))
export {}
let str = 'abcabcabcbbccccc'
let num = 0
let char = ''
let arr = ['a', 'a', 'b', 'b', 'c', 'c', 'c']
// 使其按照一定的次序排列
let compress = function (chars) {
  chars = chars.join('')
  let temp = []

  let re = /(\w)\1+/g
  chars.replace(re, ($0, $1) => {
    temp.push($1)
    temp.push(String($0.length))
    return temp
  })
  console.log(chars)
  return chars.length
}
console.log(compress(arr))
export {}
ts
function f2c(x) {
  function convert(str, p1, offset, s) {
    return ((p1 - 32) * 5) / 9 + 'C'
  }
  let s = String(x)
  let test = /(\d+(?:\.\d*)?)F\b/g
  return s.replace(test, convert)
}

console.log(f2c('232F'))
function f2c(x) {
  function convert(str, p1, offset, s) {
    return ((p1 - 32) * 5) / 9 + 'C'
  }
  let s = String(x)
  let test = /(\d+(?:\.\d*)?)F\b/g
  return s.replace(test, convert)
}

console.log(f2c('232F'))
ts
const num = 123456654321
const str = 'ABababababab'
const handle = (params) => {
  let str_1 = String(params)
    .replace(/[^0-9A-Za-z]/g, '')
    .toLowerCase()
  let str_2 = str_1.split('').reverse().join()
  return str_1 === str_2 ? true : false
}
handle(num) // true
handle(str) // false
export {}
const num = 123456654321
const str = 'ABababababab'
const handle = (params) => {
  let str_1 = String(params)
    .replace(/[^0-9A-Za-z]/g, '')
    .toLowerCase()
  let str_2 = str_1.split('').reverse().join()
  return str_1 === str_2 ? true : false
}
handle(num) // true
handle(str) // false
export {}
ts
// 三种状态
const PENDING = "pending";
const RESOLVED = "resolved";
const REJECTED = "rejected";
// promise 接收一个函数参数，该函数会立即执行
function MyPromise(fn) {
    let _this = this;
    _this.currentState = PENDING;
    _this.value = undefined;
    // 用于保存 then 中的回调，只有当 promise
    // 状态为 pending 时才会缓存，并且每个实例至多缓存一个
    _this.resolvedCallbacks = [];
    _this.rejectedCallbacks = [];

    _this.resolve = function (value) {
        if (value instanceof MyPromise) {
            // 如果 value 是个 Mypromise，递归执行
            return value.then(_this.resolve, _this.reject)
        }
        setTimeout(() => { // 异步执行，保证执行顺序
            if (_this.currentState === PENDING) {
                _this.currentState = RESOLVED;
                _this.value = value;
                _this.resolvedCallbacks.forEach(cb => cb());
            }
        })
    };

    _this.reject = function (reason) {
        setTimeout(() => { // 异步执行，保证执行顺序
            if (_this.currentState === PENDING) {
                _this.currentState = REJECTED;
                _this.value = reason;
                _this.rejectedCallbacks.forEach(cb => cb());
            }
        })
    }
    // 用于解决以下问题
    // new Mypromise(() => throw Error('error))
    try {
        fn(_this.resolve, _this.reject);
    } catch (e) {
        _this.reject(e);
    }
}

MyPromise.prototype.then = function (onResolved, onRejected) {
    let self = this;
    // 规范 2.2.7，then 必须返回一个新的 promise
    let promise2;
    // 规范 2.2.onResolved 和 onRejected 都为可选参数
    // 如果类型不是函数需要忽略，同时也实现了透传
    // Mypromise.resolve(4).then().then((value) => console.log(value))
    onResolved = typeof onResolved === 'function' ? onResolved : v => v;
    onRejected = typeof onRejected === 'function' ? onRejected : r => throw r;

    if (self.currentState === RESOLVED) {
        return (promise2 = new MyPromise(function (resolve, reject) {
            // 规范 2.2.4，保证 onFulfilled，onRjected 异步执行
            // 所以用了 setTimeout 包裹下
            setTimeout(function () {
                try {
                    let x = onResolved(self.value);
                    resolutionProcedure(promise2, x, resolve, reject);
                } catch (reason) {
                    reject(reason);
                }
            });
        }));
    }

    if (self.currentState === REJECTED) {
        return (promise2 = new MyPromise(function (resolve, reject) {
            setTimeout(function () {
                // 异步执行onRejected
                try {
                    let x = onRejected(self.value);
                    resolutionProcedure(promise2, x, resolve, reject);
                } catch (reason) {
                    reject(reason);
                }
            });
        }));
    }

    if (self.currentState === PENDING) {
        return (promise2 = new MyPromise(function (resolve, reject) {
            self.resolvedCallbacks.push(function () {
                // 考虑到可能会有报错，所以使用 try/catch 包裹
                try {
                    let x = onResolved(self.value);
                    resolutionProcedure(promise2, x, resolve, reject);
                } catch (r) {
                    reject(r);
                }
            });

            self.rejectedCallbacks.push(function () {
                try {
                    let x = onRejected(self.value);
                    resolutionProcedure(promise2, x, resolve, reject);
                } catch (r) {
                    reject(r);
                }
            });
        }));
    }
};
// 规范 2.3
function resolutionProcedure(promise2, x, resolve, reject) {
    // 规范 2.3.1，x 不能和 promise2 相同，避免循环引用
    if (promise2 === x) {
        return reject(new TypeError("Error"));
    }
    // 规范 2.3.2
    // 如果 x 为 Mypromise，状态为 pending 需要继续等待否则执行
    if (x instanceof MyPromise) {
        if (x.currentState === PENDING) {
            x.then(function (value) {
                // 再次调用该函数是为了确认 x resolve 的
                // 参数是什么类型，如果是基本类型就再次 resolve
                // 把值传给下个 then
                resolutionProcedure(promise2, value, resolve, reject);
            }, reject);
        } else {
            x.then(resolve, reject);
        }
        return;
    }
    // 规范 2.3.3.3.3
    // reject 或者 resolve 其中一个执行过得话，忽略其他的
    let called = false;
    // 规范 2.3.3，判断 x 是否为对象或者函数
    if (x !== null && (typeof x === "object" || typeof x === "function")) {
        // 规范 2.3.3.2，如果不能取出 then，就 reject
        try {
            // 规范 2.3.3.1
            let then = x.then;
            // 如果 then 是函数，调用 x.then
            if (typeof then === "function") {
                // 规范 2.3.3.3
                then.call(
                    x,
                    y => {
                        if (called) return;
                        called = true;
                        // 规范 2.3.3.3.1
                        resolutionProcedure(promise2, y, resolve, reject);
                    },
                    e => {
                        if (called) return;
                        called = true;
                        reject(e);
                    }
                );
            } else {
                // 规范 2.3.3.4
                resolve(x);
            }
        } catch (e) {
            if (called) return;
            called = true;
            reject(e);
        }
    } else {
        // 规范 2.3.4，x 为基本类型
        resolve(x);
    }
}


let p=new MyPromise(() => {
  console.log('thisis demo')
})
p.then(() => {
  console.log('lllee')
})
// 三种状态
const PENDING = "pending";
const RESOLVED = "resolved";
const REJECTED = "rejected";
// promise 接收一个函数参数，该函数会立即执行
function MyPromise(fn) {
    let _this = this;
    _this.currentState = PENDING;
    _this.value = undefined;
    // 用于保存 then 中的回调，只有当 promise
    // 状态为 pending 时才会缓存，并且每个实例至多缓存一个
    _this.resolvedCallbacks = [];
    _this.rejectedCallbacks = [];

    _this.resolve = function (value) {
        if (value instanceof MyPromise) {
            // 如果 value 是个 Mypromise，递归执行
            return value.then(_this.resolve, _this.reject)
        }
        setTimeout(() => { // 异步执行，保证执行顺序
            if (_this.currentState === PENDING) {
                _this.currentState = RESOLVED;
                _this.value = value;
                _this.resolvedCallbacks.forEach(cb => cb());
            }
        })
    };

    _this.reject = function (reason) {
        setTimeout(() => { // 异步执行，保证执行顺序
            if (_this.currentState === PENDING) {
                _this.currentState = REJECTED;
                _this.value = reason;
                _this.rejectedCallbacks.forEach(cb => cb());
            }
        })
    }
    // 用于解决以下问题
    // new Mypromise(() => throw Error('error))
    try {
        fn(_this.resolve, _this.reject);
    } catch (e) {
        _this.reject(e);
    }
}

MyPromise.prototype.then = function (onResolved, onRejected) {
    let self = this;
    // 规范 2.2.7，then 必须返回一个新的 promise
    let promise2;
    // 规范 2.2.onResolved 和 onRejected 都为可选参数
    // 如果类型不是函数需要忽略，同时也实现了透传
    // Mypromise.resolve(4).then().then((value) => console.log(value))
    onResolved = typeof onResolved === 'function' ? onResolved : v => v;
    onRejected = typeof onRejected === 'function' ? onRejected : r => throw r;

    if (self.currentState === RESOLVED) {
        return (promise2 = new MyPromise(function (resolve, reject) {
            // 规范 2.2.4，保证 onFulfilled，onRjected 异步执行
            // 所以用了 setTimeout 包裹下
            setTimeout(function () {
                try {
                    let x = onResolved(self.value);
                    resolutionProcedure(promise2, x, resolve, reject);
                } catch (reason) {
                    reject(reason);
                }
            });
        }));
    }

    if (self.currentState === REJECTED) {
        return (promise2 = new MyPromise(function (resolve, reject) {
            setTimeout(function () {
                // 异步执行onRejected
                try {
                    let x = onRejected(self.value);
                    resolutionProcedure(promise2, x, resolve, reject);
                } catch (reason) {
                    reject(reason);
                }
            });
        }));
    }

    if (self.currentState === PENDING) {
        return (promise2 = new MyPromise(function (resolve, reject) {
            self.resolvedCallbacks.push(function () {
                // 考虑到可能会有报错，所以使用 try/catch 包裹
                try {
                    let x = onResolved(self.value);
                    resolutionProcedure(promise2, x, resolve, reject);
                } catch (r) {
                    reject(r);
                }
            });

            self.rejectedCallbacks.push(function () {
                try {
                    let x = onRejected(self.value);
                    resolutionProcedure(promise2, x, resolve, reject);
                } catch (r) {
                    reject(r);
                }
            });
        }));
    }
};
// 规范 2.3
function resolutionProcedure(promise2, x, resolve, reject) {
    // 规范 2.3.1，x 不能和 promise2 相同，避免循环引用
    if (promise2 === x) {
        return reject(new TypeError("Error"));
    }
    // 规范 2.3.2
    // 如果 x 为 Mypromise，状态为 pending 需要继续等待否则执行
    if (x instanceof MyPromise) {
        if (x.currentState === PENDING) {
            x.then(function (value) {
                // 再次调用该函数是为了确认 x resolve 的
                // 参数是什么类型，如果是基本类型就再次 resolve
                // 把值传给下个 then
                resolutionProcedure(promise2, value, resolve, reject);
            }, reject);
        } else {
            x.then(resolve, reject);
        }
        return;
    }
    // 规范 2.3.3.3.3
    // reject 或者 resolve 其中一个执行过得话，忽略其他的
    let called = false;
    // 规范 2.3.3，判断 x 是否为对象或者函数
    if (x !== null && (typeof x === "object" || typeof x === "function")) {
        // 规范 2.3.3.2，如果不能取出 then，就 reject
        try {
            // 规范 2.3.3.1
            let then = x.then;
            // 如果 then 是函数，调用 x.then
            if (typeof then === "function") {
                // 规范 2.3.3.3
                then.call(
                    x,
                    y => {
                        if (called) return;
                        called = true;
                        // 规范 2.3.3.3.1
                        resolutionProcedure(promise2, y, resolve, reject);
                    },
                    e => {
                        if (called) return;
                        called = true;
                        reject(e);
                    }
                );
            } else {
                // 规范 2.3.3.4
                resolve(x);
            }
        } catch (e) {
            if (called) return;
            called = true;
            reject(e);
        }
    } else {
        // 规范 2.3.4，x 为基本类型
        resolve(x);
    }
}


let p=new MyPromise(() => {
  console.log('thisis demo')
})
p.then(() => {
  console.log('lllee')
})

map,padStart ​

js
{
  console.log(`________________________________________________`)
  console.log(`list`.padStart(8, `=`))
  let m = [2, 3, 4, 5, 6, 7333].map((x) => x.toString().padStart(10, `*`))
  console.log(m)
}
{
  console.log(`________________________________________________`)
  const cars = {
    '🚙BMW': `10`,
    '🚘Tesla': `5`,
    '🚖Lamborghini': `0`,
  }
  Object.entries(cars).map(([name, count]) => {
    //padEnd appends ' -' until the name becomes 20 characters
    //padStart prepends '0' until the count becomes 3 characters.
    console.log(`${name.padEnd(20, ` -`)} Count: ${count.padStart(3, `0`)}`)
  })
}
{
  console.log(`________________________________________________`)
  console.log(`list`.padStart(8, `=`))
  let m = [2, 3, 4, 5, 6, 7333].map((x) => x.toString().padStart(10, `*`))
  console.log(m)
}
{
  console.log(`________________________________________________`)
  const cars = {
    '🚙BMW': `10`,
    '🚘Tesla': `5`,
    '🚖Lamborghini': `0`,
  }
  Object.entries(cars).map(([name, count]) => {
    //padEnd appends ' -' until the name becomes 20 characters
    //padStart prepends '0' until the count becomes 3 characters.
    console.log(`${name.padEnd(20, ` -`)} Count: ${count.padStart(3, `0`)}`)
  })
}

function ​

js
// console.log(...[1,2,3,]);

function pushaay(array, items) {
  array.push(...items)
  console.log(array)
}
pushaay([1, 2], [3, 4, 5]) //[ 1, 2, 3, 4, 5 ]

function f(x, y, z) {
  //
}
let args = [1, 2, 3]
f(...args) //不需要apply方法

Math.max(...[23, 5, 12])
let arrbefore = [1, 2, 3]
let arrtemp = [3, 4, 5]
arrbefore.push(...arrtemp)
console.log(...`hello`)
{
  let mapa = new Map([
    [1, `one`],
    [2, `two`],
    [3, `three`],
  ])
  let arr = [...mapa.keys()] //[1,2,3]
  console.log(`hello\n${arr}`)
}
const go = function* () {
  yield 1
  yield 2
  yield 3
}
let numbers = [...go()] //[1,2,3]
{
  let arraylik = { '0': `a`, '1': `b`, '2': `c` }
  console.log(Array.from(arraylik))
}
{
  Array.from(`hello`) //等同于[...'hello']
  let nameset = new Set([`a`, `b`, `1`])
  console.log(Array.from(nameset))
}
{
  console.log(`________________________________________________`)
  console.log(Array.from([1, 3, 4], (x) => x * x))
}

{
  console.log(`________________________________________________`)
  function typefo() {
    return Array.from(arguments, (value) => typeof value) //返回数据类型
  }
}
{
  console.log(`________________________________________________`)
  let nameset = Array.of(2, 3, 4, 5, 6) //[2,3,4,5,6]
  console.log(nameset)
}
{
  console.log(`________________________________________________`)
  let ii = [1, 2, 3, 4, 5].copyWithin(0, 3, 4)
  console.log(ii)
}
{
  console.log(`________________________________________________`)
  function fv(v) {
    return v > this.age
  }
  let person = { name: `json`, age: 20 }
  let resp = [12, 45, 23, 11].find(fv, person)
  console.log(resp)
}
{
  console.log(`________________________________________________`)
  const a = [`q`, `b`, `c`].fill(3)
  console.log(a)
  let arr = new Array(3).fill({ name: `mike` })
  arr[0].name = `ben`
  console.log(arr) //赋值的是地址
}
{
  console.log(`________________________________________________`)
  let a = [1, 3, [34, 44]].flat()
  console.log(a)
  let m = [2, 3, 4].flatMap((x) => [x, x * 2])
  console.log(m)
  let n = [3, 4, 5].flatMap((x) => [[x * 2]])
  console.log(n)
}
{
  console.log(`________________________________________________`)
  //Array.from();
  let arr = Array.from({ '0': 1, '1': 2, length: 2 })
  console.log(arr) //[1,2]
  ;[1, 2, 3, 4, 5].reduce((prev, next, index, current) => {
    //prev 如果reduce传入第二个参数，prev为第二个参数；否则prev为数组第一个元素  往后累加
    //next 如果reduce传入第二个参数，next为第数组第一个元素；否则next为数组第二个元素  依次累加
    //index 函数第几次执行1开始
    //current当前数组
    return prev + next
  })
  //reduce方法简单实现
  Array.prototype.myReduce = function (cb, pre) {
    let prev = pre || this[0]
    for (let i = pre ? 0 : 1; i < this.length; i++) {
      prev = cb(prev, this[i], i, this)
    }
    return prev
  }
}

{
  console.log(`________________________________________________`)
  let result = [1, 2, 3, 4, 5].filter(function (item) {
    return item > 3
  })
  console.log(result) //[4,5]
  //filter简单实现
  Array.prototype.myFilter = function (cb) {
    let arr = []
    for (let i = 0; i < this.length; i++) {
      let item = this[i]
      if (cb(item)) arr.push(item)
    }
    return arr
  }
}
// console.log(...[1,2,3,]);

function pushaay(array, items) {
  array.push(...items)
  console.log(array)
}
pushaay([1, 2], [3, 4, 5]) //[ 1, 2, 3, 4, 5 ]

function f(x, y, z) {
  //
}
let args = [1, 2, 3]
f(...args) //不需要apply方法

Math.max(...[23, 5, 12])
let arrbefore = [1, 2, 3]
let arrtemp = [3, 4, 5]
arrbefore.push(...arrtemp)
console.log(...`hello`)
{
  let mapa = new Map([
    [1, `one`],
    [2, `two`],
    [3, `three`],
  ])
  let arr = [...mapa.keys()] //[1,2,3]
  console.log(`hello\n${arr}`)
}
const go = function* () {
  yield 1
  yield 2
  yield 3
}
let numbers = [...go()] //[1,2,3]
{
  let arraylik = { '0': `a`, '1': `b`, '2': `c` }
  console.log(Array.from(arraylik))
}
{
  Array.from(`hello`) //等同于[...'hello']
  let nameset = new Set([`a`, `b`, `1`])
  console.log(Array.from(nameset))
}
{
  console.log(`________________________________________________`)
  console.log(Array.from([1, 3, 4], (x) => x * x))
}

{
  console.log(`________________________________________________`)
  function typefo() {
    return Array.from(arguments, (value) => typeof value) //返回数据类型
  }
}
{
  console.log(`________________________________________________`)
  let nameset = Array.of(2, 3, 4, 5, 6) //[2,3,4,5,6]
  console.log(nameset)
}
{
  console.log(`________________________________________________`)
  let ii = [1, 2, 3, 4, 5].copyWithin(0, 3, 4)
  console.log(ii)
}
{
  console.log(`________________________________________________`)
  function fv(v) {
    return v > this.age
  }
  let person = { name: `json`, age: 20 }
  let resp = [12, 45, 23, 11].find(fv, person)
  console.log(resp)
}
{
  console.log(`________________________________________________`)
  const a = [`q`, `b`, `c`].fill(3)
  console.log(a)
  let arr = new Array(3).fill({ name: `mike` })
  arr[0].name = `ben`
  console.log(arr) //赋值的是地址
}
{
  console.log(`________________________________________________`)
  let a = [1, 3, [34, 44]].flat()
  console.log(a)
  let m = [2, 3, 4].flatMap((x) => [x, x * 2])
  console.log(m)
  let n = [3, 4, 5].flatMap((x) => [[x * 2]])
  console.log(n)
}
{
  console.log(`________________________________________________`)
  //Array.from();
  let arr = Array.from({ '0': 1, '1': 2, length: 2 })
  console.log(arr) //[1,2]
  ;[1, 2, 3, 4, 5].reduce((prev, next, index, current) => {
    //prev 如果reduce传入第二个参数，prev为第二个参数；否则prev为数组第一个元素  往后累加
    //next 如果reduce传入第二个参数，next为第数组第一个元素；否则next为数组第二个元素  依次累加
    //index 函数第几次执行1开始
    //current当前数组
    return prev + next
  })
  //reduce方法简单实现
  Array.prototype.myReduce = function (cb, pre) {
    let prev = pre || this[0]
    for (let i = pre ? 0 : 1; i < this.length; i++) {
      prev = cb(prev, this[i], i, this)
    }
    return prev
  }
}

{
  console.log(`________________________________________________`)
  let result = [1, 2, 3, 4, 5].filter(function (item) {
    return item > 3
  })
  console.log(result) //[4,5]
  //filter简单实现
  Array.prototype.myFilter = function (cb) {
    let arr = []
    for (let i = 0; i < this.length; i++) {
      let item = this[i]
      if (cb(item)) arr.push(item)
    }
    return arr
  }
}

from,of ​

js
{
  console.log(`________________________________________________`)

  const a1 = Array.of(1, 2, 3)
  const a2 = Array(6).fill(12)
  console.log(a1, a2)
}
{
  console.log(`________________________________________________`)
  const m = [1, 2, 3, 4].reduce(
    (accumulator, currentValue, currentIndex, array) =>
      accumulator * currentValue,
    1
  )
  console.log(m)
}
{
  console.log(`________________________________________________`)
  const a = [1, 2, 3]
  const it = a[Symbol.iterator]()
  console.log(it.next().done)
  console.log(it.next().value) //1
  console.log(it.next().value) //2
  console.log(it.next().value)
  const findResult = a.includes(1, 0)
  console.log(findResult, a.join(`*`))
  const b = Array.from(a, (x) => x % 2 === 0)
  console.log(b)
}
{
  console.log(`________________________________________________`)
  const list = [`a`, `b`, `c`]
  list.forEach((item, index) => {
    console.log(item) //Value
    console.log(index) //Index
  })
  //Index is optional
  list.forEach((item) => console.log(item))
}
{
  console.log(`________________________________________________`)
  const object = {
    name: `xiaoming`,
    age: 34,
    sex: `man`,
  }
  for (const property in object) {
    console.log(property) //Property name
    console.log(object[property]) //Property value
  }
}

{
  console.log(`________________________________________________`)
  const age = [16, 14, 18]

  const m = age.some((person) => person >= 18)
  console.log(m)
}
{
  console.log(`________________________________________________`)

  const a1 = Array.of(1, 2, 3)
  const a2 = Array(6).fill(12)
  console.log(a1, a2)
}
{
  console.log(`________________________________________________`)
  const m = [1, 2, 3, 4].reduce(
    (accumulator, currentValue, currentIndex, array) =>
      accumulator * currentValue,
    1
  )
  console.log(m)
}
{
  console.log(`________________________________________________`)
  const a = [1, 2, 3]
  const it = a[Symbol.iterator]()
  console.log(it.next().done)
  console.log(it.next().value) //1
  console.log(it.next().value) //2
  console.log(it.next().value)
  const findResult = a.includes(1, 0)
  console.log(findResult, a.join(`*`))
  const b = Array.from(a, (x) => x % 2 === 0)
  console.log(b)
}
{
  console.log(`________________________________________________`)
  const list = [`a`, `b`, `c`]
  list.forEach((item, index) => {
    console.log(item) //Value
    console.log(index) //Index
  })
  //Index is optional
  list.forEach((item) => console.log(item))
}
{
  console.log(`________________________________________________`)
  const object = {
    name: `xiaoming`,
    age: 34,
    sex: `man`,
  }
  for (const property in object) {
    console.log(property) //Property name
    console.log(object[property]) //Property value
  }
}

{
  console.log(`________________________________________________`)
  const age = [16, 14, 18]

  const m = age.some((person) => person >= 18)
  console.log(m)
}

getcount ​

js
let cars = ['BMW', 'Benz', 'Benz', 'Tesla', 'BMW', 'Toyota']
console.time('测试开发')
let carsObj = cars.reduce(function (obj, name) {
  console.log(obj)
  console.log(name)
  obj[name] = obj[name] ? ++obj[name] : 1
  return obj
}, {})
console.log(carsObj) // => { BMW: 2, Benz: 2, Tesla: 1, Toyota: 1 }
console.timeEnd('测试开发')
let cars = ['BMW', 'Benz', 'Benz', 'Tesla', 'BMW', 'Toyota']
console.time('测试开发')
let carsObj = cars.reduce(function (obj, name) {
  console.log(obj)
  console.log(name)
  obj[name] = obj[name] ? ++obj[name] : 1
  return obj
}, {})
console.log(carsObj) // => { BMW: 2, Benz: 2, Tesla: 1, Toyota: 1 }
console.timeEnd('测试开发')

compress ​

js
let compress = function (chars) {
  let char = chars[0]
  let num = 0
  let index = 0
  let numArr = []
  chars.forEach((item) => {
    if (item === char) {
      num++
    } else {
      chars[index] = char
      if (1 < num && num < 10) {
        index++
        chars[index] = String(num)
      } else if (num >= 10) {
        numArr = String(num).split('')
        numArr.forEach((n) => {
          index++
          chars[index] = String(n)
        })
      }
      index++
      char = item
      num = 1
    }
  })
  chars[index] = char
  if (1 < num && num < 10) {
    index++
    chars[index] = String(num)
  } else if (num >= 10) {
    numArr = String(num).split('')
    numArr.forEach((n) => {
      index++
      chars[index] = String(n)
    })
  }
  index++
  chars.length = index
  console.log(chars)
  return index
}

let arr = ['a', 'a', 'b', 'b', 'c', 'c', 'c']
console.log(compress(arr))
let compress = function (chars) {
  let char = chars[0]
  let num = 0
  let index = 0
  let numArr = []
  chars.forEach((item) => {
    if (item === char) {
      num++
    } else {
      chars[index] = char
      if (1 < num && num < 10) {
        index++
        chars[index] = String(num)
      } else if (num >= 10) {
        numArr = String(num).split('')
        numArr.forEach((n) => {
          index++
          chars[index] = String(n)
        })
      }
      index++
      char = item
      num = 1
    }
  })
  chars[index] = char
  if (1 < num && num < 10) {
    index++
    chars[index] = String(num)
  } else if (num >= 10) {
    numArr = String(num).split('')
    numArr.forEach((n) => {
      index++
      chars[index] = String(n)
    })
  }
  index++
  chars.length = index
  console.log(chars)
  return index
}

let arr = ['a', 'a', 'b', 'b', 'c', 'c', 'c']
console.log(compress(arr))

reduce ​

js
let data = {
  rows: [
    ['Lisa', 16, 'Female', '2000-12-01'],
    ['Bob', 22, 'Male', '1996-01-21'],
  ],
  metaData: [
    {
      name: 'name',
      note: '',
    },
    {
      name: 'age',
      note: '',
    },
    {
      name: 'gender',
      note: '',
    },
    {
      name: 'birthday',
      note: '',
    },
  ],
}

let result = data.rows.reduce(function (prev1, cur1) {
  prev1.push(
    data.metaData.reduce(function (prev, cur, index) {
      prev[cur.name] = cur1[index]
      return prev
    }, {})
  )
  return prev1
}, [])

console.log(result)
console.log(result[0])
console.log(result[1])

export {}
let data = {
  rows: [
    ['Lisa', 16, 'Female', '2000-12-01'],
    ['Bob', 22, 'Male', '1996-01-21'],
  ],
  metaData: [
    {
      name: 'name',
      note: '',
    },
    {
      name: 'age',
      note: '',
    },
    {
      name: 'gender',
      note: '',
    },
    {
      name: 'birthday',
      note: '',
    },
  ],
}

let result = data.rows.reduce(function (prev1, cur1) {
  prev1.push(
    data.metaData.reduce(function (prev, cur, index) {
      prev[cur.name] = cur1[index]
      return prev
    }, {})
  )
  return prev1
}, [])

console.log(result)
console.log(result[0])
console.log(result[1])

export {}

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