Javascript小白经典题型(二)

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"

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]

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: 1 2 and 3 3 and 6 4
• B: 1 2 and 2 3 and 3 4
• C: 1 undefined and 2 undefined and 3 undefined and 4 undefined
• D: 1 2 and undefined 3 and undefined 4

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;
  }
  //
  constructor(name, size) {
    super(name);
    this.size = size;
  }
  //
  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 answer = yield "Do you love JavaScript?";
  if (answer !== "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

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

79. 输出什么?

const myLifeSummedUp = ["?", "??", "??", "??"]

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

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

• A: 0 1 2 3 and "?" "??" "??" "??"
• B: "?" "??" "??" "??" and "?" "??" "??" "??"
• C: "?" "??" "??" "??" and 0 1 2 3
• D: 0 1 2 3 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

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"

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: name Lydia and age 21
• 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

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

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

原文链接：https://github.com/lydiahallie/javascript-questions/blob/master/zh-CN/README-zh_CN.md