javascript有意思的题

相信大家一面试才会想起刷力扣力扣官网，今天没那么麻烦， 记录一下一些有意思的题，懒得翻译了，直接看题库吧，想要了解更多，请走电梯

1. What's the output?

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

sayHi();

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

2. What's the output?

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 and 0 1 2
• B: 0 1 2 and 3 3 3
• C: 3 3 3 and 0 1 2

3. What's the output?

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

console.log(shape.diameter());
console.log(shape.perimeter());

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

4. What's the output?

+true;
!'Lydia';

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

5. Which one is true?

const bird = {
  size: 'small',
};

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

• A: mouse.bird.size is not valid
• B: mouse[bird.size] is not valid
• C: mouse[bird["size"]] is not valid
• D: All of them are valid

6. What's the output?

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

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

• A: Hello
• B: Hey!
• C: undefined
• D: ReferenceError
• E: TypeError

7. What's the output?

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

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

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

8. What's the output?

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

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

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

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

9. What's the output?

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

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

10. What happens when we do this?

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

bark.animal = 'dog';

• A: Nothing, this is totally fine!
• B: SyntaxError. You cannot add properties to a function this way.
• C: "Woof" gets logged.
• D: ReferenceError