JavaScript二十道经典面试题+答案解析

1. 下面代码的输出是什么? +true;!"Lydia";

    * A: 1 and false

    * B: false and NaN

    * C: false and false

 

2. 下面代码的输出是什么？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

 3. 下面代码的输出是什么?

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 and 0 1 2

    * B: 0 1 2 and 3 3 3

    * C: 3 3 3 and 0 1 2

 

4. 下面代码的输出是什么?

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