2025年最新笔试题

zijie

1.  下列输出什么结果

undefined == false; // true
undefined === false; // false
[] == []; // false
[] === []; // false
{} == {}; // Uncaught SyntaxError: Unexpected token '=='
{} === {}; // Uncaught SyntaxError: Unexpected token '==='

2.  找到字符串中，第一个不重复字符，存在的话，返回这个字符的序号；如果不存在，则返回-1；

/*** 如：* s = leetcode  return 0;* s = love leetcode return 2; * s = aabb return -1; */
const str = 'leetcode';
// (.)捕获一个字符
// (?=.*\\1)是一个正向先行断言，表示在当前位置之后存在于捕获组\\1(即前面捕获的字符)相同的字符
// g 标志标识全局匹配,这样可以匹配字符串中所有重复的字符
let reg = new RegExp('(.)(?=.*\\1)', 'g');
// 从原始字符串中去除所有匹配到的重复字符串,得到了不重复的字符
const nonRepeatedChars = str.replace(reg, '');
console.log(nonRepeatedChars);
const firstChart = nonRepeatedChars.length > 0 ? nonRepeatedChars[0] : null;

3. 根据数据动态画出dom元素

const data = {tagName: 'ul',props: {'class': 'list'},children: [{tagName: 'li', children: ['douyin']},{tagName: 'li', children: ['toutiao']}]
};
<ul class="list"><li>douyin</li><li>toutiao</li>
</ul>

const createEl = (item, parentEl) => {        const node = document.createElement(item.tagName);if (item.props) {const cls = Object.keys(item.props)[0];node.setAttribute(cls, item.props[cls]);}const childrenList = item?.children;const isString = Array.isArray(childrenList) && childrenList.length > 0 &&typeof childrenList[0] === 'string';if (isString) {node.textContent = childrenList[0];}parentEl.appendChild(node);if (!isString) {childrenList.forEach(child => {createEl(child, node);});}
}
createEl(data, document.body);

4. 以下代码执行结果

第一道题

async function async1() {console.log("async1");await async2();console.log("async1 end");
}
async function async2() {console.log("async2");
}
console.log("script start");
setTimeout(() => {console.log("setTimeout");
},0)
async1();
new Promise(() => {console.log("promise1");
}).then(() => {console.log("promise2");
})
console.log("script end");输出结果：
script start
async1
async2
promise1
script endasync1 end
promise2
setTimeout

第二道题

console.log('script start');
var asyncFn = async() => {await new Promise((resolve) => {console.log("asyncFn");resolve();}).then(() => {console.log("asyncFn promise1");})console.log("asyncFn end");
};
asyncFn();
setTimeout(function() {console.log("setTimeout");
}, 0);
new Promise((resolve) => {console.log("Promise");resolve();
}).then(function(){console.log("promise1");
}).then(function() {console.log("promise2");
});
console.log("script end");输出结果：
script start
asyncFn
Promise
script endasyncFn promise1
promise1
asyncFn end
promise2
setTimeout

 

5. 给下列版本排序 

var versions = ["1.45.0", "1.5", "1.2.5", "3.3.3.3.3", "6"];

注意：1.45.0小于1.5

 

meituan

 1. 手动实现数组的 flat 方法（ES2019提供的方法）

Array.prototype.myFlat = function(depth = 1) {const result = [];for(const item of this) {if (Array.isArray(item) && depth > 0) {// 递归调用 myFlat 方法，深度减1result.push(...item.myFlat(depth -1));}else {result.push(item);}}return result;
}
const arr = [1,3,4,[5,6,[7,8]]];
console.log(arr.myFlat(2));

2. npm包版本比较，如果 version1 > version2 返回 1，如果 version1 < version2 返回 -1，其他情况返回0

比如：1.2.3 vs 1.2；

　　　1.2.3 vs 3.4.1

const compareVersion = (version1,version2) => {const firstArr = version1.split('.');const sencondArr = version2.split('.');const length = Math.max(firstArr.length, sencondArr.length); // 取最大的长度for(let i = 0; i < length;i++) {const v1Part = i < firstArr.length ? firstArr[i] : 0;const v2Part = i < sencondArr.length ? sencondArr[i] : 0;if (v1Part > v2Part) {return 1;}else if (v1Part < v2Part) {return -1;}}return 0
}
const result = compareVersion('1.2.3','1.2');
console.log(result);

其他常见笔试题

1. 手写一个函数，模拟JS中的new操作符

function myNew(constructor,...args) {const obj = {};obj.__proto__ = constructor.prototype;const result = constructor.apply(obj, args);return typeof result === 'object' && result !== null ? result : obj;
}
function Person(name,age) {this.name = name;this.age = age;
}
Person.prototype.sayHello = function() {console.log(`hello, my name is ${this.name} and I'm ${this.age} years old.`);
}
const person = myNew(Person, 'Alice', 30);
person.sayHello();

 

2. 实现一个函数，将驼峰命名法的字符串转换为下划线命名法

function camelToSnake(str) {const snakeStr = str.replace(/[A-Z]/g, (match) => {return '_' + match.toLowerCase();})return snakeStr.replace(/^_/, '');
}
const camelCase = 'HelloWorldJavaScript';
console.log(camelToSnake(camelCase));