面试手写第六期

本文主要是介绍面试手写第六期，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

一. Promise封装Ajax请求

function getJSON(url) {return new Promise((resolve, reject) => {let xhr = new XMLHttpRequest();// 新建一个HTTP请求xhr.open('get', url, true);// 设置状态的监听函数xhr.onreadystatechange = function () {if (this.readyState !== 4) return;if (this.status === 200) {resolve(this.response);} else {reject(new Error(this.statusText));}};xhr.onerror = function () {reject(new Error(this.statusText));};xhr.responseType = 'json';xhr.setRequestHeader('Accept', 'application/json');xhr.send(null);});
}

二. setTimeout实现setInterval

function mySetTimeout(func, delay) {let timer = null;const interval = () => {func();timer = setTimeout(interval, delay);};setTimeout(interval, delay);return {cancel: () => {clearTimeout(timer);},};
}const { cancel } = mySetTimeout(() => console.log('999'), 1000);setTimeout(() => {cancel();
}, 4000);

三. js对象转换为树结构

function arrayToTreeRec(nodes) {const map = {};const tree = [];for (const node of nodes) {node[node.id] = { ...node, children: [] };}for (const node of Object.values(map)) {if (node.parentId === null) {tree.push(node);} else {map[node.parentId].children.push(node);}}return tree;
}

四. 实现JSON.stringfy方法

function jsonStringify(obj) {// 处理非对象类型，直接返回对应的字符串形式if (typeof obj !== 'object' || obj === null) {// 处理字符串类型if (typeof obj === 'string') {console.log(obj);return '"' + obj + '"';}return String(obj);}// 处理数组类型if (Array.isArray(obj)) {const result = [];for (let i = 0; i < obj.length; i++) {result.push(jsonStringify(obj[i]));}return '[' + result.join(',') + ']';}// 处理对象类型const result = [];for (let key in obj) {if (obj.hasOwnProperty(key)) {const value = jsonStringify(obj[key]);// 处理 undefined、函数和 symbol 属性值if (value !== undefined) {const prop = '"' + key + '":' + value;result.push(prop);}}}return '{' + result.join(',') + '}';
}let obj = {name: 'zs',age: 18,hobby: ['1', '2', '3']
}
console.log(jsonStringify(obj));

五. new操作符的实现

function _new(obj, ...rest){// 基于obj的原型创建一个新的对象const newObj = Object.create(obj.prototype);// 添加属性到新创建的newObj上, 并获取obj函数执行的结果.const result = obj.apply(newObj, rest);// 如果执行结果有返回值并且是一个对象, 返回执行的结果, 否则, 返回新创建的对象return typeof result === 'object' ? result : newObj;
}

六. 数组去重的几种方法

1. 两层for循环

function unique(arr) {let len = arr.lengthfor(let i = 0; i < len; i++) {for(let j = i + 1; j < len; j++) {if(arr[i] == arr[j]) {arr.splice(j, 1)j--len--}}}return arr
}

2. filter + indexOf

function unique(arr) {return arr.filter((item, index) => {return arr.indexOf(item) == index})
}

3. 创建新数组 + includes

function unique(arr) {let newArr = []for(let i = 0; i < arr.length; i++) {if(!newArr.includes(arr[i])) {newArr.push(arr[i])}}return newArr
}

4. indexOf实现

function unique(arr) {let newArr = []for(let i = 0; i < arr.length; i++) {if(newArr.indexOf(arr[i]) === -1) {newArr.push(arr[i])}}return newArr
}

5. Set实现

function unique(arr) {return [...new Set(arr)]
}

七. 大数相加

function add(str1, str2) {let maxLength = Math.max(str1.length, str2.length)str1 = str1.padStart(maxLength, 0)str2 = str2.padStart(maxLength, 0)let temp = 0let flag = 0 // 余数let result = ''for(let i = maxLength - 1; i >= 0; i--) {temp = str1[i] + str2[i] + flagflag = Math.floor(temp / 10)result = temp % 10 + result}if(flag == 1) {result = '1' + result}return result
}let a = "9876543210123456789000000000123";
let b = "1234567898765432100000012345678901";
console.log(add(a, b));

八. 大数相乘

function multiplyStrings(num1, num2) {const len1 = num1.length;const len2 = num2.length;const result = new Array(len1 + len2).fill(0); // 结果数组初始化为0for (let i = len1 - 1; i >= 0; i--) {for (let j = len2 - 1; j >= 0; j--) {const product = Number(num1[i]) * Number(num2[j]); // 计算当前位的乘积const sum = result[i + j + 1] + product; // 当前位的和等于之前的结果加上当前位乘积result[i + j + 1] = sum % 10; // 保存当前位的数值result[i + j] += Math.floor(sum / 10); // 进位}}// 去掉结果前面的0while (result[0] === 0 && result.length > 1) {result.shift();}return result.join(''); // 将结果转为字符串返回
}let a = "123";
let b = "456";
console.log(multiplyStrings(a, b));

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