# JavaScript 进阶问题列表

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我在我的 Instagram 上每天都会发布 JavaScript 的多选问题，并且同时也会在这个仓库中发布。

从基础到进阶，测试你有多了解 JavaScript，刷新你的知识，或者帮助你的 coding 面试！ 💪 🚀 我每周都会在这个仓库下更新新的问题。

答案在问题下方的折叠部分，点击即可展开问题。祝你好运 ❤️

# 1. 输出是什么？

function sayHi() {
  console.log(name)
  console.log(age)
  var name = 'Lydia'
  let age = 21
}

sayHi()

• A: Lydia 和 undefined
• B: Lydia 和 ReferenceError
• C: ReferenceError 和 21
• D: undefined 和 ReferenceError

# 2. 输出是什么？

for (var i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 1)
}

for (let i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 1)
}

• A: 0 1 2 和 0 1 2
• B: 0 1 2 和 3 3 3
• C: 3 3 3 和 0 1 2

# 3. 输出是什么？

const shape = {
  radius: 10,
  diameter() {
    return this.radius * 2
  },
  perimeter: () => 2 * Math.PI * this.radius
}

shape.diameter()
shape.perimeter()

• A: 20 and 62.83185307179586
• B: 20 and NaN
• C: 20 and 63
• D: NaN and 63

# 4. 输出是什么？

+true;
!"Lydia";

• A: 1 and false
• B: false and NaN
• C: false and false

# 5. 哪一个是正确的？

const bird = {
  size: 'small'
}

const mouse = {
  name: 'Mickey',
  small: true
}

• A: mouse.bird.size是无效的
• B: mouse[bird.size]是无效的
• C: mouse[bird["size"]]是无效的
• D: 以上三个选项都是有效的

# 6. 输出是什么？

let c = { greeting: 'Hey!' }
let d

d = c
c.greeting = 'Hello'
console.log(d.greeting)

• A: Hello
• B: undefined
• C: ReferenceError
• D: TypeError

答案

# 答案: A

在 JavaScript 中，当设置两个对象彼此相等时，它们会通过引用进行交互。

首先，变量 c 的值是一个对象。接下来，我们给 d 分配了一个和 c 对象相同的引用。

因此当我们改变其中一个对象时，其实是改变了所有的对象。

# 7. 输出是什么？

let a = 3
let b = new Number(3)
let c = 3

console.log(a == b)
console.log(a === b)
console.log(b === c)

• A: truefalsetrue
• B: falsefalsetrue
• C: truefalsefalse
• D: falsetruetrue

# 8. 输出是什么？

class Chameleon {
  static colorChange(newColor) {
    this.newColor = newColor
    return this.newColor
  }

  constructor({ newColor = 'green' } = {}) {
    this.newColor = newColor
  }
}

const freddie = new Chameleon({ newColor: 'purple' })
freddie.colorChange('orange')

• A: orange
• B: purple
• C: green
• D: TypeError

# 9. 输出是什么？

let greeting
greetign = {} // Typo!
console.log(greetign)

• A: {}
• B: ReferenceError: greetign is not defined
• C: undefined

# 10. 当我们这么做时，会发生什么？

function bark() {
  console.log('Woof!')
}

bark.animal = 'dog'

• A: 正常运行!
• B: SyntaxError. 你不能通过这种方式给函数增加属性。
• C: undefined
• D: ReferenceError

# 11. 输出是什么？

function Person(firstName, lastName) {
  this.firstName = firstName;
  this.lastName = lastName;
}

const member = new Person("Lydia", "Hallie");
Person.getFullName = function () {
  return `${this.firstName} ${this.lastName}`;
}

console.log(member.getFullName());

• A: TypeError
• B: SyntaxError
• C: Lydia Hallie
• D: undefinedundefined

Person.prototype.getFullName = function () {
  return `${this.firstName} ${this.lastName}`;
}

# 12. 输出是什么？

function Person(firstName, lastName) {
  this.firstName = firstName
  this.lastName = lastName
}

const lydia = new Person('Lydia', 'Hallie')
const sarah = Person('Sarah', 'Smith')

console.log(lydia)
console.log(sarah)

• A: Person {firstName: "Lydia", lastName: "Hallie"} and undefined
• B: Person {firstName: "Lydia", lastName: "Hallie"} and Person {firstName: "Sarah", lastName: "Smith"}
• C: Person {firstName: "Lydia", lastName: "Hallie"} and {}
• D:Person {firstName: "Lydia", lastName: "Hallie"} and ReferenceError

# 13. 事件传播的三个阶段是什么？

• A: Target > Capturing > Bubbling
• B: Bubbling > Target > Capturing
• C: Target > Bubbling > Capturing
• D: Capturing > Target > Bubbling

答案

# 答案: D

在捕获（capturing）阶段中，事件从祖先元素向下传播到目标元素。当事件达到目标（target）元素后，冒泡（bubbling）才开始。

# 14. 所有对象都有原型。

• A: 对
• B: 错

# 15. 输出是什么？

function sum(a, b) {
  return a + b
}

sum(1, '2')

• A: NaN
• B: TypeError
• C: "12"
• D: 3

# 16. 输出是什么？

let number = 0
console.log(number++)
console.log(++number)
console.log(number)

• A: 112
• B: 122
• C: 022
• D: 012

# 17. 输出是什么？

function getPersonInfo(one, two, three) {
  console.log(one)
  console.log(two)
  console.log(three)
}

const person = 'Lydia'
const age = 21

getPersonInfo`${person} is ${age} years old`

• A: "Lydia"21["", " is ", " years old"]
• B: ["", " is ", " years old"]"Lydia"21
• C: "Lydia"["", " is ", " years old"]21

# 18. 输出是什么？

function checkAge(data) {
  if (data === { age: 18 }) {
    console.log('You are an adult!')
  } else if (data == { age: 18 }) {
    console.log('You are still an adult.')
  } else {
    console.log(`Hmm.. You don't have an age I guess`)
  }
}

checkAge({ age: 18 })

• A: You are an adult!
• B: You are still an adult.
• C: Hmm.. You don't have an age I guess

# 19. 输出是什么？

function getAge(...args) {
  console.log(typeof args)
}

getAge(21)

• A: "number"
• B: "array"
• C: "object"
• D: "NaN"

# 20. 输出是什么？

function getAge() {
  'use strict'
  age = 21
  console.log(age)
}

getAge()

• A: 21
• B: undefined
• C: ReferenceError
• D: TypeError

# 21. 输出是什么？

const sum = eval('10*10+5')

• A: 105
• B: "105"
• C: TypeError
• D: "10*10+5"

# 22. cool_secret 可访问多长时间？

sessionStorage.setItem('cool_secret', 123)

• A: 永远，数据不会丢失。
• B: 当用户关掉标签页时。
• C: 当用户关掉整个浏览器，而不只是关掉标签页。
• D: 当用户关闭电脑时。

# 23. 输出是什么？

var num = 8
var num = 10

console.log(num)

• A: 8
• B: 10
• C: SyntaxError
• D: ReferenceError

# 24. 输出是什么？

const obj = { 1: 'a', 2: 'b', 3: 'c' }
const set = new Set([1, 2, 3, 4, 5])

obj.hasOwnProperty('1')
obj.hasOwnProperty(1)
set.has('1')
set.has(1)

• A: falsetruefalsetrue
• B: falsetruetruetrue
• C: truetruefalsetrue
• D: truetruetruetrue

# 25. 输出是什么？

const obj = { a: 'one', b: 'two', a: 'three' }
console.log(obj)

• A: { a: "one", b: "two" }
• B: { b: "two", a: "three" }
• C: { a: "three", b: "two" }
• D: SyntaxError

# 26. JavaScript 全局执行上下文为你做了两件事：全局对象和 this 关键字。

• A: 对
• B: 错
• C: 看情况

# 27. 输出是什么？

for (let i = 1; i < 5; i++) {
  if (i === 3) continue
  console.log(i)
}

• A: 12
• B: 123
• C: 124
• D: 134

# 28. 输出是什么？

String.prototype.giveLydiaPizza = () => {
  return 'Just give Lydia pizza already!'
}

const name = 'Lydia'

name.giveLydiaPizza()

• A: "Just give Lydia pizza already!"
• B: TypeError: not a function
• C: SyntaxError
• D: undefined

# 29. 输出是什么？

const a = {}
const b = { key: 'b' }
const c = { key: 'c' }

a[b] = 123
a[c] = 456

console.log(a[b])

• A: 123
• B: 456
• C: undefined
• D: ReferenceError

# 30. 输出是什么？

const foo = () => console.log('First')
const bar = () => setTimeout(() => console.log('Second'))
const baz = () => console.log('Third')

bar()
foo()
baz()

• A: FirstSecondThird
• B: FirstThirdSecond
• C: SecondFirstThird
• D: SecondThirdFirst

答案

# 答案: B

我们有一个 setTimeout 函数，并首先调用它。然而，它是最后打印日志的。

这是因为在浏览器中，我们不仅有运行时引擎，还有一个叫做 WebAPI 的东西。WebAPI 提供了 setTimeout 函数，也包含其他的，例如 DOM。

将 callback 推送到 WebAPI 后，setTimeout 函数本身(但不是回调！)将从栈中弹出。

现在，foo 被调用，打印 "First"。

foo 从栈中弹出，baz 被调用. 打印 "Third"。

WebAPI 不能随时向栈内添加内容。相反，它将回调函数推到名为 queue 的地方。

这就是事件循环开始工作的地方。一个事件循环查看栈和任务队列。如果栈是空的，它接受队列上的第一个元素并将其推入栈。

bar 被调用，打印 "Second"，然后它被栈弹出。

# 31. 当点击按钮时，event.target是什么？

<div onclick="console.log('first div')">
  <div onclick="console.log('second div')">
    <button onclick="console.log('button')">
      Click!
    </button>
  </div>
</div>

• A: Outer div
• B: Inner div
• C: button
• D: 一个包含所有嵌套元素的数组。

# 32. 当您单击该段落时，日志输出是什么？

<div onclick="console.log('div')">
  <p onclick="console.log('p')">
    Click here!
  </p>
</div>

• A: pdiv
• B: divp
• C: p
• D: div

# 33. 输出是什么？

const person = { name: 'Lydia' }

function sayHi(age) {
  console.log(`${this.name} is ${age}`)
}

sayHi.call(person, 21)
sayHi.bind(person, 21)

• A: undefined is 21Lydia is 21
• B: functionfunction
• C: Lydia is 21Lydia is 21
• D: Lydia is 21function

# 34. 输出是什么？

function sayHi() {
  return (() => 0)()
}

typeof sayHi()

• A: "object"
• B: "number"
• C: "function"
• D: "undefined"

# 35. 下面哪些值是 falsy?

0
new Number(0)
('')
(' ')
new Boolean(false)
undefined

• A: 0, '', undefined
• B: 0, new Number(0), '', new Boolean(false), undefined
• C: 0, '', new Boolean(false), undefined
• D: All of them are falsy

# 36. 输出是什么？

console.log(typeof typeof 1)

• A: "number"
• B: "string"
• C: "object"
• D: "undefined"

# 37. 输出是什么？

const numbers = [1, 2, 3]
numbers[10] = 11
console.log(numbers)

• A: [1, 2, 3, 7 x null, 11]
• B: [1, 2, 3, 11]
• C: [1, 2, 3, 7 x empty, 11]
• D: SyntaxError

# 38. 输出是什么？

(() => {
  let x, y
  try {
    throw new Error()
  } catch (x) {
    (x = 1), (y = 2)
    console.log(x)
  }
  console.log(x)
  console.log(y)
})()

• A: 1undefined2
• B: undefinedundefinedundefined
• C: 112
• D: 1undefinedundefined

# 39. JavaScript 中的一切都是？

• A: 基本类型与对象
• B: 函数与对象
• C: 只有对象
• D: 数字与对象

# 40. 输出是什么？

[[0, 1], [2, 3]].reduce(
  (acc, cur) => {
    return acc.concat(cur)
  },
  [1, 2]
)

• A: [0, 1, 2, 3, 1, 2]
• B: [6, 1, 2]
• C: [1, 2, 0, 1, 2, 3]
• D: [1, 2, 6]

# 41. 输出是什么？

!!null
!!''
!!1

• A: falsetruefalse
• B: falsefalsetrue
• C: falsetruetrue
• D: truetruefalse

# 42. setInterval 方法的返回值是什么？

setInterval(() => console.log('Hi'), 1000)

• A: 一个唯一的id
• B: 该方法指定的毫秒数
• C: 传递的函数
• D: undefined

# 43. 输出是什么？

[...'Lydia']

• A: ["L", "y", "d", "i", "a"]
• B: ["Lydia"]
• C: [[], "Lydia"]
• D: [["L", "y", "d", "i", "a"]]

# 44. 输出是什么?

function* generator(i) {
  yield i;
  yield i * 2;
}

const gen = generator(10);

console.log(gen.next().value);
console.log(gen.next().value);

• A: [0, 10], [10, 20]
• B: 20, 20
• C: 10, 20
• D: 0, 10 and 10, 20

# 45. 返回值是什么?

const firstPromise = new Promise((res, rej) => {
  setTimeout(res, 500, "one");
});

const secondPromise = new Promise((res, rej) => {
  setTimeout(res, 100, "two");
});

Promise.race([firstPromise, secondPromise]).then(res => console.log(res));

• A: "one"
• B: "two"
• C: "two" "one"
• D: "one" "two"

# 46. 输出是什么?

let person = { name: "Lydia" };
const members = [person];
person = null;

console.log(members);

• A: null
• B: [null]
• C: [{}]
• D: [{ name: "Lydia" }]

答案

# 答案: D

首先我们声明了一个拥有name属性的对象 person。

然后我们又声明了一个变量members. 将首个元素赋值为变量person。 当设置两个对象彼此相等时，它们会通过 引用 进行交互。但是当你将引用从一个变量分配至另一个变量时，其实只是执行了一个 复制 操作。（注意一点，他们的引用 并不相同!）

接下来我们让person等于null。

我们没有修改数组第一个元素的值，而只是修改了变量person的值,因为元素（复制而来）的引用与person不同。members的第一个元素仍然保持着对原始对象的引用。当我们输出members数组时，第一个元素会将引用的对象打印出来。

# 47. 输出是什么?

const person = {
  name: "Lydia",
  age: 21
};

for (const item in person) {
  console.log(item);
}

• A: { name: "Lydia" }, { age: 21 }
• B: "name", "age"
• C: "Lydia", 21
• D: ["name", "Lydia"], ["age", 21]

# 48. 输出是什么?

console.log(3 + 4 + "5");

• A: "345"
• B: "75"
• C: 12
• D: "12"

# 49. num的值是什么?

const num = parseInt("7*6", 10);

• A: 42
• B: "42"
• C: 7
• D: NaN

# 50. 输出是什么?

[1, 2, 3].map(num => {
  if (typeof num === "number") return;
  return num * 2;
});

• A: []
• B: [null, null, null]
• C: [undefined, undefined, undefined]
• D: [ 3 x empty ]

# 51. 输出的是什么?

function getInfo(member, year) {
  member.name = "Lydia";
  year = "1998";
}

const person = { name: "Sarah" };
const birthYear = "1997";

getInfo(person, birthYear);

console.log(person, birthYear);

• A: { name: "Lydia" }, "1997"
• B: { name: "Sarah" }, "1998"
• C: { name: "Lydia" }, "1998"
• D: { name: "Sarah" }, "1997"

# 52. 输出是什么?

function greeting() {
  throw "Hello world!";
}

function sayHi() {
  try {
    const data = greeting();
    console.log("It worked!", data);
  } catch (e) {
    console.log("Oh no an error:", e);
  }
}

sayHi();

• A: "It worked! Hello world!"
• B: "Oh no an error: undefined
• C: SyntaxError: can only throw Error objects
• D: "Oh no an error: Hello world!

# 53. 输出是什么?

function Car() {
  this.make = "Lamborghini";
  return { make: "Maserati" };
}

const myCar = new Car();
console.log(myCar.make);

• A: "Lamborghini"
• B: "Maserati"
• C: ReferenceError
• D: TypeError

# 54. 输出是什么?

(() => {
  let x = (y = 10);
})();

console.log(typeof x);
console.log(typeof y);

• A: "undefined", "number"
• B: "number", "number"
• C: "object", "number"
• D: "number", "undefined"

y = 10;
let x = y;

#55. 输出是什么?

class Dog {
  constructor(name) {
    this.name = name;
  }
}

Dog.prototype.bark = function() {
  console.log(`Woof I am ${this.name}`);
};

const pet = new Dog("Mara");

pet.bark();

delete Dog.prototype.bark;

pet.bark();

• A: "Woof I am Mara", TypeError
• B: "Woof I am Mara","Woof I am Mara"
• C: "Woof I am Mara", undefined
• D: TypeError, TypeError

# 56. 输出是什么?

const set = new Set([1, 1, 2, 3, 4]);

console.log(set);

• A: [1, 1, 2, 3, 4]
• B: [1, 2, 3, 4]
• C: {1, 1, 2, 3, 4}
• D: {1, 2, 3, 4}

# 57. 输出是什么?

// counter.js
let counter = 10;
export default counter;

// index.js
import myCounter from "./counter";

myCounter += 1;

console.log(myCounter);

• A: 10
• B: 11
• C: Error
• D: NaN

# 58. 输出是什么?

const name = "Lydia";
age = 21;

console.log(delete name);
console.log(delete age);

• A: false, true
• B: "Lydia", 21
• C: true, true
• D: undefined, undefined

# 59. 输出是什么?

const numbers = [1, 2, 3, 4, 5];
const [y] = numbers;

console.log(y);

• A: [[1, 2, 3, 4, 5]]
• B: [1, 2, 3, 4, 5]
• C: 1
• D: [1]

答案

# 答案: C

我们可以通过解构赋值来解析来自对象的数组或属性的值，比如说：

[a, b] = [1, 2];

a的值现在是1，b的值现在是2.而在题目中，我们是这么做的:

[y] = [1, 2, 3, 4, 5];

也就是说，y等于数组的第一个值就是数字1.我们输出y， 返回1.

# 60. 输出是什么?

const user = { name: "Lydia", age: 21 };
const admin = { admin: true, ...user };

console.log(admin);

• A: { admin: true, user: { name: "Lydia", age: 21 } }
• B: { admin: true, name: "Lydia", age: 21 }
• C: { admin: true, user: ["Lydia", 21] }
• D: { admin: true }

# 61. 输出是什么?

const person = { name: "Lydia" };

Object.defineProperty(person, "age", { value: 21 });

console.log(person);
console.log(Object.keys(person));

• A: { name: "Lydia", age: 21 }, ["name", "age"]
• B: { name: "Lydia", age: 21 }, ["name"]
• C: { name: "Lydia"}, ["name", "age"]
• D: { name: "Lydia"}, ["age"]

# 62. 输出是什么?

const settings = {
  username: "lydiahallie",
  level: 19,
  health: 90
};

const data = JSON.stringify(settings, ["level", "health"]);
console.log(data);

• A: "{"level":19, "health":90}"
• B: "{"username": "lydiahallie"}"
• C: "["level", "health"]"
• D: "{"username": "lydiahallie", "level":19, "health":90}"

# 63. 输出是什么?

let num = 10;

const increaseNumber = () => num++;
const increasePassedNumber = number => number++;

const num1 = increaseNumber();
const num2 = increasePassedNumber(num1);

console.log(num1);
console.log(num2);

• A: 10, 10
• B: 10, 11
• C: 11, 11
• D: 11, 12

# 64. 输出什么?

const value = { number: 10 };

const multiply = (x = { ...value }) => {
  console.log(x.number *= 2);
};

multiply();
multiply();
multiply(value);
multiply(value);

• A: 20, 40, 80, 160
• B: 20, 40, 20, 40
• C: 20, 20, 20, 40
• D: NaN, NaN, 20, 40

# 65. 输出什么?

[1, 2, 3, 4].reduce((x, y) => console.log(x, y));

• A: 12 and 33 and 64
• B: 12 and 23 and 34
• C: 1undefined and 2undefined and 3undefined and 4undefined
• D: 12 and undefined3 and undefined4

# 66. 使用哪个构造函数可以成功继承Dog类?

class Dog {
  constructor(name) {
    this.name = name;
  }
};

class Labrador extends Dog {
  // 1 
  constructor(name, size) {
    this.size = size;
  }
  // 2
  constructor(name, size) {
    super(name);
    this.size = size;
  }
  // 3
  constructor(size) {
    super(name);
    this.size = size;
  }
  // 4 
  constructor(name, size) {
    this.name = name;
    this.size = size;
  }

};

• A: 1
• B: 2
• C: 3
• D: 4

# 67. 输出什么?

// index.js
console.log('running index.js');
import { sum } from './sum.js';
console.log(sum(1, 2));

// sum.js
console.log('running sum.js');
export const sum = (a, b) => a + b;

• A: running index.js, running sum.js, 3
• B: running sum.js, running index.js, 3
• C: running sum.js, 3, running index.js
• D: running index.js, undefined, running sum.js

# 68. 输出什么?

console.log(Number(2) === Number(2))
console.log(Boolean(false) === Boolean(false))
console.log(Symbol('foo') === Symbol('foo'))

• A: true, true, false
• B: false, true, false
• C: true, false, true
• D: true, true, true

# 69. 输出什么?

const name = "Lydia Hallie"
console.log(name.padStart(13))
console.log(name.padStart(2))

• A: "Lydia Hallie", "Lydia Hallie"
• B: " Lydia Hallie", " Lydia Hallie" ("[13x whitespace]Lydia Hallie", "[2x whitespace]Lydia Hallie")
• C: " Lydia Hallie", "Lydia Hallie" ("[1x whitespace]Lydia Hallie", "Lydia Hallie")
• D: "Lydia Hallie", "Lyd"

# 70. 输出什么?

console.log("🥑" + "💻");

• A: "🥑💻"
• B: 257548
• C: A string containing their code points
• D: Error

# 71. 如何能打印出console.log语句后注释掉的值？

function* startGame() {
  const 答案 = yield "Do you love JavaScript?";
  if (答案 !== "Yes") {
    return "Oh wow... Guess we're gone here";
  }
  return "JavaScript loves you back ❤️";
}

const game = startGame();
console.log(/* 1 */); // Do you love JavaScript?
console.log(/* 2 */); // JavaScript loves you back ❤️

• A: game.next("Yes").value and game.next().value
• B: game.next.value("Yes") and game.next.value()
• C: game.next().value and game.next("Yes").value
• D: game.next.value() and game.next.value("Yes")

# 72. 输出什么?

console.log(String.raw`Hello\nworld`);

• A: Hello world!
• B: Hello
world
• C: Hello\nworld
• D: Hello\n
world

const path = `C:\Documents\Projects\table.html`
String.raw`${path}`

String.raw`C:\Documents\Projects\table.html`

# 73. 输出什么?

async function getData() {
  return await Promise.resolve("I made it!");
}

const data = getData();
console.log(data);

• A: "I made it!"
• B: Promise {<resolved>: "I made it!"}
• C: Promise {<pending>}
• D: undefined

# 74. 输出什么?

function addToList(item, list) {
  return list.push(item);
}

const result = addToList("apple", ["banana"]);
console.log(result);

• A: ['apple', 'banana']
• B: 2
• C: true
• D: undefined

# 75. 输出什么?

const box = { x: 10, y: 20 };

Object.freeze(box);

const shape = box;
shape.x = 100;
console.log(shape)

• A: { x: 100, y: 20 }
• B: { x: 10, y: 20 }
• C: { x: 100 }
• D: ReferenceError

# 76. 输出什么?

const { name: myName } = { name: "Lydia" };

console.log(name);

• A: "Lydia"
• B: "myName"
• C: undefined
• D: ReferenceError

# 77. 以下是个纯函数么?

function sum(a, b) {
  return a + b;
}

• A: Yes
• B: No

# 78. 输出什么?

const add = () => {
  const cache = {};
  return num => {
    if (num in cache) {
      return `From cache! ${cache[num]}`;
    } else {
      const result = num + 10;
      cache[num] = result;
      return `Calculated! ${result}`;
    }
  };
};

const addFunction = add();
console.log(addFunction(10));
console.log(addFunction(10));
console.log(addFunction(5 * 2));

• A: Calculated! 20Calculated! 20Calculated! 20
• B: Calculated! 20From cache! 20Calculated! 20
• C: Calculated! 20From cache! 20From cache! 20
• D: Calculated! 20From cache! 20Error

#79. 输出什么?

const myLifeSummedUp = ["☕", "💻", "🍷", "🍫"]

for (let item in myLifeSummedUp) {
  console.log(item)
}

for (let item of myLifeSummedUp) {
  console.log(item)
}

• A: 0123 and "☕""💻""🍷""🍫"
• B: "☕""💻""🍷""🍫" and "☕""💻""🍷""🍫"
• C: "☕""💻""🍷""🍫" and 0123
• D: 0123 and {0: "☕", 1: "💻", 2: "🍷", 3: "🍫"}

# 80. 输出什么?

const list = [1 + 2, 1 * 2, 1 / 2]
console.log(list)

• A: ["1 + 2", "1 * 2", "1 / 2"]
• B: ["12", 2, 0.5]
• C: [3, 2, 0.5]
• D: [1, 1, 1]

# 81. 输出什么?

function sayHi(name) {
  return `Hi there, ${name}`
}

console.log(sayHi())

• A: Hi there,
• B: Hi there, undefined
• C: Hi there, null
• D: ReferenceError

# 82. 输出什么?

var status = "😎"

setTimeout(() => {
  const status = "😍"

  const data = {
    status: "🥑",
    getStatus() {
      return this.status
    }
  }

  console.log(data.getStatus())
  console.log(data.getStatus.call(this))
}, 0)

• A: "🥑" and "😍"
• B: "🥑" and "😎"
• C: "😍" and "😎"
• D: "😎" and "😎"

# 83. 输出什么?

const person = {
  name: "Lydia",
  age: 21
}

let city = person.city
city = "Amsterdam"

console.log(person)

• A: { name: "Lydia", age: 21 }
• B: { name: "Lydia", age: 21, city: "Amsterdam" }
• C: { name: "Lydia", age: 21, city: undefined }
• D: "Amsterdam"

# 84. 输出什么?

function checkAge(age) {
  if (age < 18) {
    const message = "Sorry, you're too young."
  } else {
    const message = "Yay! You're old enough!"
  }

  return message
}

console.log(checkAge(21))

• A: "Sorry, you're too young."
• B: "Yay! You're old enough!"
• C: ReferenceError
• D: undefined

# 85. 什么样的信息将被打印?

fetch('https://www.website.com/api/user/1')
  .then(res => res.json())
  .then(res => console.log(res))

• A: fetch方法的结果
• B: 第二次调用fetch方法的结果
• C: 前一个.then()中回调方法返回的结果
• D: 总是undefined

# 86. 哪个选项是将hasName设置为true的方法，前提是不能将true作为参数传递?

function getName(name) {
  const hasName = //
}

• A: !!name
• B: name
• C: new Boolean(name)
• D: name.length

# 87. 输出什么?

console.log("I want pizza"[0])

• A: """
• B: "I"
• C: SyntaxError
• D: undefined

# 88. 输出什么?

function sum(num1, num2 = num1) {
  console.log(num1 + num2)
}

sum(10)

• A: NaN
• B: 20
• C: ReferenceError
• D: undefined

function test(m = n, n = 2) {
	console.log(m, n)
}
test() // Uncaught ReferenceError: Cannot access 'n' before initialization
test(3) // 3 2
test(3, 4) // 3 4

# 89. 输出什么?

// module.js 
export default () => "Hello world"
export const name = "Lydia"

// index.js 
import * as data from "./module"

console.log(data)

• A: { default: function default(), name: "Lydia" }
• B: { default: function default() }
• C: { default: "Hello world", name: "Lydia" }
• D: Global object of module.js

# 90. 输出什么?

class Person {
  constructor(name) {
    this.name = name
  }
}

const member = new Person("John")
console.log(typeof member)

• A: "class"
• B: "function"
• C: "object"
• D: "string"

function Person() {
  this.name = name
}

# 91. 输出什么?

let newList = [1, 2, 3].push(4)

console.log(newList.push(5))

• A: [1, 2, 3, 4, 5]
• B: [1, 2, 3, 5]
• C: [1, 2, 3, 4]
• D: Error

# 92. 输出什么?

function giveLydiaPizza() {
  return "Here is pizza!"
}

const giveLydiaChocolate = () => "Here's chocolate... now go hit the gym already."

console.log(giveLydiaPizza.prototype)
console.log(giveLydiaChocolate.prototype)

• A: { constructor: ...}{ constructor: ...}
• B: {}{ constructor: ...}
• C: { constructor: ...}{}
• D: { constructor: ...}undefined

# 93. 输出什么?

const person = {
  name: "Lydia",
  age: 21
}

for (const [x, y] of Object.entries(person)) {
  console.log(x, y)
}

• A: nameLydia and age21
• B: ["name", "Lydia"] and ["age", 21]
• C: ["name", "age"] and undefined
• D: Error

# 94. 输出什么?

function getItems(fruitList, ...args, favoriteFruit) {
  return [...fruitList, ...args, favoriteFruit]
}

getItems(["banana", "apple"], "pear", "orange")

• A: ["banana", "apple", "pear", "orange"]
• B: [["banana", "apple"], "pear", "orange"]
• C: ["banana", "apple", ["pear"], "orange"]
• D: SyntaxError

function getItems(fruitList, favoriteFruit, ...args) {
  return [...fruitList, ...args, favoriteFruit]
}

getItems(["banana", "apple"], "pear", "orange")

#95. 输出什么?

function nums(a, b) {
  if
  (a > b)
  console.log('a is bigger')
  else 
  console.log('b is bigger')
  return 
  a + b
}

console.log(nums(4, 2))
console.log(nums(1, 2))

• A: a is bigger, 6 and b is bigger, 3
• B: a is bigger, undefined and b is bigger, undefined
• C: undefined and undefined
• D: SyntaxError

  return;
  a + b

# 96. 输出什么?

class Person {
  constructor() {
    this.name = "Lydia"
  }
}

Person = class AnotherPerson {
  constructor() {
    this.name = "Sarah"
  }
}

const member = new Person()
console.log(member.name)

• A: "Lydia"
• B: "Sarah"
• C: Error: cannot redeclare Person
• D: SyntaxError

# 97. 输出什么?

const info = {
  [Symbol('a')]: 'b'
}

console.log(info)
console.log(Object.keys(info))

• A: {Symbol('a'): 'b'} and ["{Symbol('a')"]
• B: {} and []
• C: { a: "b" } and ["a"]
• D: {Symbol('a'): 'b'} and []

# 98. 输出什么?

const getList = ([x, ...y]) => [x, y]
const getUser = user => { name: user.name, age: user.age }

const list = [1, 2, 3, 4]
const user = { name: "Lydia", age: 21 }

console.log(getList(list))
console.log(getUser(user))

• A: [1, [2, 3, 4]] and undefined
• B: [1, [2, 3, 4]] and { name: "Lydia", age: 21 }
• C: [1, 2, 3, 4] and { name: "Lydia", age: 21 }
• D: Error and { name: "Lydia", age: 21 }

# 99. 输出什么?

const name = "Lydia"

console.log(name())

• A: SyntaxError
• B: ReferenceError
• C: TypeError
• D: undefined

# 100. 输出什么?

// 🎉✨ This is my 100th question! ✨🎉

const output = `${[] && 'Im'}possible!
You should${'' && `n't`} see a therapist after so much JavaScript lol`

• A: possible! You should see a therapist after so much JavaScript lol
• B: Impossible! You should see a therapist after so much JavaScript lol
• C: possible! You shouldn't see a therapist after so much JavaScript lol
• D: Impossible! You shouldn't see a therapist after so much JavaScript lol

# 101.输出什么?

const one = (false || {} || null)
const two = (null || false || "")
const three = ([] || 0 || true)

console.log(one, two, three)

• A: falsenull[]
• B: null""true
• C: {}""[]
• D: nullnulltrue

# 102. 依次输出什么?

const myPromise = () => Promise.resolve('I have resolved!')

function firstFunction() {
  myPromise().then(res => console.log(res))
  console.log('second')
}

async function secondFunction() {
  console.log(await myPromise())
  console.log('second')
}

firstFunction()
secondFunction()

• A: I have resolved!, second and I have resolved!, second
• B: second, I have resolved! and second, I have resolved!
• C: I have resolved!, second and second, I have resolved!
• D: second, I have resolved! and I have resolved!, second

# 103. 输出什么?

const set = new Set()

set.add(1)
set.add("Lydia")
set.add({ name: "Lydia" })

for (let item of set) {
  console.log(item + 2)
}

• A: 3, NaN, NaN
• B: 3, 7, NaN
• C: 3, Lydia2, [Object object]2
• D: "12", Lydia2, [Object object]2

# 104. 结果是什么?

Promise.resolve(5)

• A: 5
• B: Promise {<pending>: 5}
• C: Promise {<resolved>: 5}
• D: Error

# 105. 输出什么?

function compareMembers(person1, person2 = person) {
  if (person1 !== person2) {
    console.log("Not the same!")
  } else {
    console.log("They are the same!")
  }
}

const person = { name: "Lydia" }

compareMembers(person)

• A: Not the same!
• B: They are the same!
• C: ReferenceError
• D: SyntaxError

# 106. 输出什么?

const colorConfig = {
  red: true,
  blue: false,
  green: true,
  black: true,
  yellow: false,
}

const colors = ["pink", "red", "blue"]

console.log(colorConfig.colors[1])

• A: true
• B: false
• C: undefined
• D: TypeError

# 107. 输出什么?

console.log('❤️' === '❤️')

• A: true
• B: false

# 108. 哪些方法修改了原数组?

const emojis = ['✨', '🥑', '😍']

emojis.map(x => x + '✨')
emojis.filter(x => x !== '🥑')
emojis.find(x => x !== '🥑')
emojis.reduce((acc, cur) => acc + '✨')
emojis.slice(1, 2, '✨') 
emojis.splice(1, 2, '✨')

• A: All of them
• B: mapreduceslicesplice
• C: mapslicesplice
• D: splice

#109. 输出什么?

const food = ['🍕', '🍫', '🥑', '🍔']
const info = { favoriteFood: food[0] }

info.favoriteFood = '🍝'

console.log(food)

• A: ['🍕', '🍫', '🥑', '🍔']
• B: ['🍝', '🍫', '🥑', '🍔']
• C: ['🍝', '🍕', '🍫', '🥑', '🍔']
• D: ReferenceError

# 110. 这个函数干了什么?

JSON.parse()

• A: Parses JSON to a JavaScript value
• B: Parses a JavaScript object to JSON
• C: Parses any JavaScript value to JSON
• D: Parses JSON to a JavaScript object only

// 将数字字符串化为有效的JSON，然后将JSON字符串解析为JavaScript值:
const jsonNumber = JSON.stringify(4) // '4'
JSON.parse(jsonNumber) // 4

// 将数组值字符串化为有效的JSON，然后将JSON字符串解析为JavaScript值:
const jsonArray = JSON.stringify([1, 2, 3]) // '[1, 2, 3]'
JSON.parse(jsonArray) // [1, 2, 3]

// 将对象字符串化为有效的JSON，然后将JSON字符串解析为JavaScript值:
const jsonArray = JSON.stringify({ name: "Lydia" }) // '{"name":"Lydia"}'
JSON.parse(jsonArray) // { name: 'Lydia' }

# 111. 输出什么?

let name = 'Lydia'

function getName() {
  console.log(name)
  let name = 'Sarah'
}

getName()

• A: Lydia
• B: Sarah
• C: undefined
• D: ReferenceError

let name = 'Lydia'

function getName() {
  console.log(name)
}

getName() // Lydia

# 112. 输出什么？

function* generatorOne() {
  yield ['a', 'b', 'c'];
}

function* generatorTwo() {
  yield* ['a', 'b', 'c'];
}

const one = generatorOne()
const two = generatorTwo()

console.log(one.next().value)
console.log(two.next().value)

• A: a and a
• B: a and undefined
• C: ['a', 'b', 'c'] and a
• D: a and ['a', 'b', 'c']

console.log(one.next().value) // ['a', 'b', 'c']
console.log(one.next().value) // undefined

console.log(two.next().value) // 'a'
console.log(two.next().value) // 'b'
console.log(two.next().value) // 'c'
console.log(two.next().value) // undefined

# 113. 输出什么？

console.log(`${(x => x)('I love')} to program`)

• A: I love to program
• B: undefined to program
• C: ${(x => x)('I love') to program
• D: TypeError

# 114. 将会发生什么?

let config = {
  alert: setInterval(() => {
    console.log('Alert!')
  }, 1000)
}

config = null

• A: setInterval 的回调不会被调用
• B: setInterval 的回调被调用一次
• C: setInterval 的回调仍然会被每秒钟调用
• D: 我们从没调用过 config.alert(), config 为 null

# 115. 哪一个方法会返回 'Hello world!' ？

const myMap = new Map()
const myFunc = () => 'greeting'

myMap.set(myFunc, 'Hello world!')

//1
myMap.get('greeting')
//2
myMap.get(myFunc)
//3
myMap.get(() => 'greeting')

• A: 1
• B: 2
• C: 2 and 3
• D: All of them

# 116. 输出什么？

const person = {
  name: "Lydia",
  age: 21
}

const changeAge = (x = { ...person }) => x.age += 1
const changeAgeAndName = (x = { ...person }) => {
  x.age += 1
  x.name = "Sarah"
}

changeAge(person)
changeAgeAndName()

console.log(person)

• A: {name: "Sarah", age: 22}
• B: {name: "Sarah", age: 23}
• C: {name: "Lydia", age: 22}
• D: {name: "Lydia", age: 23}

# 117. 下面那个选项将会返回 6?

function sumValues(x, y, z) {
	return x + y + z;
}

• A: sumValues([...1, 2, 3])
• B: sumValues([...[1, 2, 3]])
• C: sumValues(...[1, 2, 3])
• D: sumValues([1, 2, 3])

# 118. 输出什么？

let num = 1;
const list = ["🥳", "🤠", "🥰", "🤪"];

console.log(list[(num += 1)]);

• A: 🤠
• B: 🥰
• C: SyntaxError
• D: ReferenceError

# 119. 输出什么？

const person = {
	firstName: "Lydia",
	lastName: "Hallie",
	pet: {
		name: "Mara",
		breed: "Dutch Tulip Hound"
	},
	getFullName() {
		return `${this.firstName} ${this.lastName}`;
	}
};

console.log(person.pet?.name);
console.log(person.pet?.family?.name);
console.log(person.getFullName?.());
console.log(member.getLastName?.());

• A: undefinedundefinedundefinedundefined
• B: MaraundefinedLydia Hallieundefined
• C: MaranullLydia Hallienull
• D: nullReferenceErrornullReferenceError