0.下面代碼輸出是什么？
// 0 '' null false undefined
console.log(0 == '',0 == null,0 == false,0 == undefined)
console.log('' == null,'' == false,'' == undefined)
console.log(null == false,null == undefined,false == undefined)
console.log(!0,!'',!null,!false,!undefined)
console.log(+0,+'',+null,+false,+undefined)
console.log(-0,-'',-null,-false,-undefined)
console.log(~0,~'',~null,~false,~undefined)
console.log(~~0,~~'',~~null,~~false,~~undefined)
1.下面代碼輸出是什么打厘？
function sayHi(){
console.log(name);
console.log(age);
var name = 'me';
let age = 18;
}
sayHi()
2.下面代碼輸出是什么蚪缀？
let name = 'me';
{
console.log(name);
let name = 'code';
}
3.下面代碼輸出是什么秫逝？
const shape = {
radius: 10,
diameter(){
return this.radius * 2
},
perimeter: () => 2 * Math.PI * this.radius
}
console.log(shape.diameter());
console.log(shape.perimeter());
4.下面代碼輸出是什么？
console.log(+true);
console.log(!'linda');
5.下面代碼輸出是什么询枚？
const bird = {
size: 'small'
}
const mouse = {
name: 'Mickey',
small: true
}
console.log(mouse.bird.size)
console.log(mouse[bird.size])
console.log(mouse[bird['size']])
6.下面代碼輸出是什么违帆？
let c = {
greeting: 'hey',
}
let d;
d = c;
c.greeting = 'hello';
console.log(d.greeting);
7.下面代碼輸出是什么？
let a = 3;
let b = new Number(3);
let c = 3;
console.log(a == b);
console.log(a === b);
console.log(b === c);
console.log(a === c);
8.下面代碼輸出是什么金蜀？
class Chameleon {
static colorChange(newColor){
this.newColor = newColor
}
constructor({newColor='green'} = {}) {
this.newColor = newColor
}
}
const freddie = new Chameleon({newColor:'purple'});
console.log(freddie.colorChange('orange'));
9.下面代碼輸出是什么刷后？
// 'use strict'
let greeting;
greetign = {};
console.log(greetign)
10.下面代碼輸出是什么？
function bark(){
console.log('Woof')
}
bark.animal = 'dog'
console.log(bark.animal)
11.下面代碼輸出是什么渊抄？
function Person(firstName,lastName){
this.firstName = firstName;
this.lastName = lastName;
}
const member = new Person('Linda','Harlin');
Person.getFullName = () => this.firstName + this.lastName;
// Person.prototype.getFullName = function(){
// return `${this.firstName} ${this.lastName}`
// }
console.log(member.getFullName());
12.下面代碼輸出是什么尝胆？
function Person(firstName,lastName){
this.firstName = firstName;
this.lastName = lastName;
}
const Linda = new Person('Linda','Harlin');
const Sarah = Person('Sarah','Smith');
console.log(Linda)
console.log(Sarah)
13.事件傳播的三個(gè)階段是什么？
// 捕獲->目標(biāo)->冒泡
14.所有對(duì)象都有原型护桦？
// 錯(cuò)誤
// 除基礎(chǔ)對(duì)象外含衔，所有對(duì)象都有原型《郑基礎(chǔ)對(duì)象的原型是null
15.下面代碼輸出是什么抱慌？
function sum(a,b){
return a + b;
}
console.log(sum(1,'2'))
16.下面代碼輸出是什么？
let number = 0;
console.log(number++);
console.log(++number);
console.log(number);
17.下面代碼輸出是什么眨猎？
function getPersonInfo(one,two,three){
console.log(one)
console.log(two)
console.log(three)
}
const person = 'Linda';
const age = 18;
console.log(getPersonInfo`${person} is ${age} year old`)
18.下面代碼輸出是什么？
function checkAge(data){
if(data==={age:18}){
console.log('A')
} else if(data=={age:18}){
console.log('B')
}else{
console.log('C')
}
}
console.log(checkAge({age:18}))
19.下面代碼輸出是什么强经？
function getAge(...args){
console.log(args)
console.log(typeof args)
}
console.log(getAge(21));
20.下面代碼輸出是什么睡陪？
function getAge(){
'use strict';
age = 18;
console.log(age)
}
console.log(getAge());
21.下面代碼輸出是什么？
const sum = eval('10*10+5')
console.log(sum)
22.cool_secret可以訪問(wèn)多長(zhǎng)時(shí)間匿情？
sessionStorage.setItem('cool_secret',123);
// 用戶關(guān)閉選項(xiàng)卡時(shí)清除
23.下面代碼輸出是什么兰迫？
var num = 8;
var num = 10;
console.log(num);
24.下面代碼輸出是什么？
const obj = {1:'a',2:'b',3:'c'};
const set = new Set([1,2,3,4,5]);
console.log(obj.hasOwnProperty('1'));
console.log(obj.hasOwnProperty(1));
console.log(set.has('1'));
console.log(set.has(1));
25.下面代碼輸出是什么炬称？
const obj = {a:'one',b:'two',a:'three'};
console.log(obj)
// 如果對(duì)象有兩個(gè)具有相同名稱的鍵汁果，則將替換前面的鍵。它仍將處于第一個(gè)位置玲躯，但具有最后指定的值
26.JavaScript全局執(zhí)行上下文為你創(chuàng)建了兩個(gè)東西...
// 全局對(duì)象和this關(guān)鍵字
27.下面代碼輸出是什么据德？
for (let i = 0; i < 5; i++) {
if(i===3) continue;
console.log(i)
}
// 如果某個(gè)條件返回 true ，則 continue 語(yǔ)句跳過(guò)迭代
28.下面代碼輸出是什么跷车？
String.prototype.giveLindaPizza = () => {
return 'ddd'
}
const name = 'Linda';
console.log(name.giveLindaPizza())
29.下面代碼輸出是什么棘利？
const a = {};
const b = {key:'b'};
const c = {key:'c'};
a[b] = 123;
a[c] = 456;
console.log(a[b]);
// a["[object Object]"] = 123
// a["[object Object]"] = 456
30.下面代碼輸出是什么？
const foo = () => console.log('1')
const bar = () => setTimeout(() => console.log('2'))
const baz = () => console.log('3')
console.log(foo())
console.log(bar())
console.log(baz())
31.單擊按鈕時(shí) event.target 是什么朽缴？
<div onclick="console.log('1')">
<div onclick="console.log('2')">
<button onclick="console.log('3')">
Click!
</button>
</div>
</div>
// button
32.單擊下面 html 片段打印的內(nèi)容是什么善玫？
<div onclick="console.log('div')">
<p onclick="console.log('p')">
Click here!
</div>
// p div
33.下面代碼輸出是什么？
const person = {name:'Linda'};
function sayHi(age){
console.log(`${this.name} id ${age}`)
}
console.log(sayHi.call(person,18));
console.log(sayHi.bind(person,18));
34.下面代碼輸出是什么密强？
function sayHi() {
return (() => 0)();
}
// console.log(sayHi());
console.log(typeof sayHi());
35.以上哪些是假值茅郎？
0;
new Number(0);
('');
(' ');
new Boolean(false);
undefined;
// JavaScript 中只有6個(gè)假值：
undefined null NaN 0 '' false
36.下面代碼輸出是什么蜗元？
console.log(typeof typeof 1);
37.下面代碼輸出是什么？
const numbers = [1,2,3];
numbers[10] = 11;
console.log(numbers)
38.下面代碼輸出是什么系冗？
(() => {
let x,y;
try{
throw new Error();
}catch(x){
(x=1),(y=2);
console.log(x);
}
console.log(x);
console.log(y);
})()
39.JavaScript 中的所有內(nèi)容都是...
// 原始和對(duì)象
// JavaScript 只有原始類型和對(duì)象
// 原始類型是
Boolean null undefined BigInt Number String Symbol
40.下面代碼輸出是什么奕扣？
[[0,1],[2,3]].reduce(
(acc,cur) => {
return acc.concat(cur);
},
[1,2]
)
41.下面代碼輸出是什么？
console.log(!!null);
console.log(!!'');
console.log(!!1);
42.下面方法返回值是什么毕谴？
setInterval(() => console.log('Hi'),1000);
// 一個(gè)唯一的id 可使用 claerInterval(id) 清除定時(shí)器
43.下面代碼輸出是什么成畦？
console.log([...'Linda']);
44.TypeError、ReferenceError涝开、SyntaxError的區(qū)別
// ReferenceError是跟作用域判別失敗有關(guān)
// TypeError是作用域判別成功后對(duì)結(jié)果非法操作或者不合理
// TypeError 對(duì)一個(gè)變量的值做不合理的操作,如對(duì)非函數(shù)的變量進(jìn)行函數(shù)調(diào)用
// 或者引用null或undefined類型的值得屬性
let a = {};
console.log(a.list.name); //這種情況也比較常出現(xiàn)
