2020最新：100道有答案的前端面试题（下）

["1", "2", "3"].map(parseInt);

[typeof null, null instanceof Object]

function f() {}
const a = f.prototype,b = Object.getPrototypeOf(f)
console.log(a === b);

function showCase(value) {
    switch(value) {
    case 'A':
        console.log('Case A');
        break;
    case 'B':
        console.log('Case B');
        break;
    case undefined:
        console.log('undefined');
        break;
    default:
        console.log('Do not know!');
    }
}
showCase(new String('A'));

console.log([2,1,0].reduce(Math.pow));
console.log([].reduce(Math.pow));

/ *
A. 2 报错
B. 2 NaN
C. 1 报错
D. 1 NaN
*/

function test(){
    var a = 1;
    return function(){
        eval("");
    }
}
test();  

const value  = 'Value is' + !!Number(['0']) ? 'yideng' : 'undefined';
console.log(value);

var arr = [0,1];
arr[5] = 5;
newArr = arr.filter(function(x) { return x === undefined;});
console.log(newArr.length);

async function async1() {
    console.log('async1 start');
    await async2();
    console.log('async1 end');
}
async function async2() {
 console.log('async2');
}
console.log('script start');
setTimeout(function() {
    console.log('setTimeout');
}, 0)
async1();
new Promise(function(resolve) {
    console.log('promise1');
    resolve();
}).then(function() {
    console.log('promise2');
});
console.log('script end');

var a = ?;
if(a == 1 && a== 2 && a== 3){
  console.log(1);
}

const obj = {
    '2': 3,
    '3': 4,
    'length': 2,
    'splice': Array.prototype.splice,
    'push': Array.prototype.push
}
obj.push(1)
obj.push(2)
console.log(obj)

let yd = { x: 1, y: 2 };
// 以下两段代码会抛出异常吗？
let ydWithXGetter1 = {
  ...yd,
  get x() {
    throw new Error();
  },
};

let ydWithXGetter2 = {
  ...yd,
  ...{
    get x() {
      throw new Error();
    },
  },
};

const arrLike = {
  length:4,
  0:0,
  1:1,
  '-1':2,
  3:3,
  4:4,
}
console.log(Array.from(arrLike));
console.log(Array.prototype.slice.call(arrLike));

let ydObject = { ...null, ...undefined };
console.log(ydObject);
let ydArray = [...null, ...undefined];
console.log(ydArray);

 function foo(){
   console.log(length);
 }
function bar(){
  var length = "京程一灯";
  foo();
}
bar();

var obj = {};
var x = +obj.yideng?.name ?? '京程一灯';
console.log(x);

let a = [];
let b = "0";
console.log(a == 0);
console.log(a == !a);
console.log(b == 0);
console.log(a == b);

const arr1 = ['a', 'b', 'c'];
const arr2 = ['b', 'c', 'a'];
console.log(
  arr1.sort() === arr1,
  arr2.sort() == arr2,
  arr1.sort() === arr2.sort()
);

console.log(null == 0);
console.log(null <= 0);
console.log(null < 0);

/*
 *示例：
 *给定数组：[2,6,3,8,10,9]
 *返回数组：[6,8,8,10,-1,-1]
 */

function getResult(data,n,sum){
  // your code
}

/*
 *有下边这样的dom结构，现在可以获取到ul，要求翻转里边li标签，如何处理更优
 */
<ul>
  <li>1</li>
  <li>2</li>
  <li>3</li>
</ul>