js 手写函数

unshift()

const arr = [1, 2.3];
arr.myUnshift(4, 5, 6);
Array.prototype.myUnshift = function () {
  const len = arguments.length;
  for (let i = len - 1; i >= 0; i--) {
    this.slice(0, 0, arguments[i]);
  }
  return this.length;
};

console.log(arr.myUnshift(4, 5, 6), arr);

去重

//(method) Array<any>.indexOf(searchElement: any, fromIndex?: number | undefined): number

Array.prototype.myUnique = function () {
  return this.filter((v, idx) => {
    return this.indexOf(v, 0) === idx;
  });
};

或

Array.prototype.myUnique = function () {
  return [...new Set(this)];
};

获取指定范围内的随机数

function fn(min, max) {
  //(min,max)
  //   return Math.round(Math.random() * (max - min - 2) + (min + 1));
  //[min,max]
  //   return Math.round(Math.random() * (max - min ) + min);
  //(min,max)
  //   return Math.ceil(Math.random() * (max - min) + (min));
  //(min,max)
  return Math.floor(Math.random() * (max - min) + min);
}

打印 100 之内的质数

let count;
for (let i = 2; i < 100; i++) {
  for (let j = 1; j <= i; j++) {
    if (i % j === 0) {
      count++;
    }
  }
  //质数只能被1和它本身整除
  if (count === 2) {
    console.log(i);
  }
  count = 0;
}

如何提取 URL 中的参数

const url = "https://baidu.com?a=1&b=2&c=3#hash";
function queryURLParams(URL) {
  let url = URL.split("?")[1];
  const urlSearchParams = new URLSearchParams(url);
  const params = Object.fromEntries(urlSearchParams.entries());
  return params;
}
console.log(queryURLParams(url));

数组随机排序

function result(arr) {
  for (let i = 0; i < arr.length; i++) {
    let randomIndex = parseInt(Math.random() * arr.length);

    let curNum = arr[i];
    arr[i] = arr[randomIndex];
    arr[randomIndex] = curNum;
  }
  return arr;
}

或

const arr = [1, 2, 3, 4, 5, 6, 7, 8];
arr.sort(() => Math.random() - 0.5);
console.log(arr);

实现迭代的方式实现 flatten

let arr = [1, 2, [3, 4, 5], 6, [7, [8, 9, [10, [11, 12]]]]];

const flatten = function (arr) {
  while (arr.some((v) => Array.isArray(v))) {
    arr = [].concat(...arr);
  }
  return arr;
};

或

const flatten = function (arr) {
  return [].concat(...arr.map((v) => (Array.isArray(v) ? flatten(v) : v)));
};

两数之和

// nums target

const nums = [2, 7, 11, 17];
const target = 9;
function twoSum(nums, target) {
  for (let i = 0; i < nums.length; i++) {
    const targetIndex = nums.indexOf(target - nums[i]);
    if (targetIndex > -1 && targetIndex !== i) {
      return [i, targetIndex];
    }
  }
}

给 a,b,c 三个请求，c 在 a,b 获取完数据之后再发送请求

// 1. promise.all

const fs = require("fs");
let arr = [];
function fn(data) {
  arr.push(data);
  if (arr.length === 2) {
    console.log(arr);
  }
}

fs.readFile("./a.text", "utf-8", (err, data) => {
  fn(data);
});

fs.readFile("./b.text", "utf-8", (err, data) => {
  fn(data);
});

如何实现一个事件发布订阅

class EventEmitter {
  handlers = {};
  on(type, handler, once = false) {
    if (!this.handlers[type]) {
      this.handlers[type] = [];
    }
    if (!this.handlers[type].includes(handler)) {
      this.handlers[type].push(handler);
      handler.once = once;
    }
  }
  once(type, handler) {
    this.on(type, handler, true);
  }
  off(type, handler) {
    if (this.handlers[type]) {
      this.handlers[type] = this.handlers[type].filter((h) => h !== handler);
    }
  }
  trigger(type) {
    if (this.handlers[type]) {
      this.handlers[type].forEach((handler) => {
        handler.call(this);
        if (handler.once) {
          this.off(type, handler);
        }
      });
    }
  }
}

const ev = new EventEmitter();
function handler1() {
  console.log("handler1");
}
function handler2() {
  console.log("handler2");
}
function handler3() {
  console.log("handler3");
}

ev.on("test", handler1);
ev.once("test", handler2);
ev.on("test", handler3);

ev.trigger("test");
ev.trigger("test");

apply、call、bind

apply

Function.prototype.myApply = function (context, args) {
  context = context || window;
  context.fn = this;
  let result = context.fn(...args);
  delete context.fn;
  return result;
};

call

Function.prototype.myCall = function (context, ...args) {
  context = context || window;
  context.fn = this;
  let result = context.fn(...args);
  delete context.fn;
  return result;
};

bind

Function.prototype.myBind = function (context, ...arg1) {
  let that = this;
  return function (...arg2) {
    return that.apply(context, [...arg1, ...arg2]);
  };
};

Promise.all

Promise.all = function (promises) {
  return new Promise((resolve, reject) => {
    if (typeof promises[Symbol.iterator] !== "function") {
      reject("Type error");
    }

    if (promises.length === 0) {
      resolve([]);
    } else {
      const res = [];
      let count = 0;
      const len = promises.length;
      for (let i = 0; i < len; i++) {
        Promise.resolve(promises[i])
          .then((data) => {
            res[i] = data;
            if (++count === len) {
              resolve[res];
            }
          })
          .catch((err) => {
            reject(err);
          });
      }
    }
  });
};

instanceof

function myInstanceof(target, origin) {
  if (typeof target !== "object" || target === null) return false;

  if (typeof origin !== "function")
    throw new TypeError("origin must be function");

  let proto = Object.getPrototypeOf(target);
  while (proto) {
    if (proto === origin.prototype) return true;
    proto = Object.getPrototypeOf(proto);
  }
  return false;
}

reduce

Array.prototype.reduce = function (cb, initialValue) {
  let arr = this,
    total = arr[0] || initialValue;

  for (let i = initialValue ? 0 : 1; i < arr.length; i++) {
    cb(total, arr[i], i, arr);
  }
  return total;
};