JavaScript面试题收集

以下题目大多数为输出题目，正确答案输出一下即可，其余的在百度上都能搜到答案，我就不贴答案了。

1. 根据以下程序打印输出值，为什么？严格模式下输出是什么？为什么?

var a = function(){
  this.b = 3;
}
var c = new a();
a.prototype.b = 9;
var b = 7;
a();
console.log(b);
console.log(c.b); 

2. 给定一个升序整型数组[0,1,2,4,5,7,13,15,16],找出其中连续出现的数字区间，输出为["0->2","4->5","7","13","15->16"]

function formatArrToRange(arr){
  //logic
}

3. 下面代码的输出结果

function A(x){
  this.x = x;
}
A.prototype.x = 1;

function B(x){
  this.x = x;
}
B.prototype = new A();

const b = new B(3)
delete b.x;
console.log(b.x)

4. 以下三段代码的输出

var x = 1;
function func(x,y=function(){x=2}){
  x = 3;
  y();
  console.log(x)
}
func(5)
console.log(x)

var x = 1;
function func(x,y=function(){x=2}){
  var x = 3;
  y();
  console.log(x)
}
func(5)
console.log(x)

var x = 1;
function func(x,y=function(){x=2}){
  var x = 3;
  var y = function(){x=4}
  y();
  console.log(x)
}
func(5)
console.log(x)

5. 以下关于Promise代码输出

const promise = new Promise((resolve, reject) => {
    console.log(1)
    resolve()
    console.log(2)
})
promise.then(() => {
    console.log(3)
})
console.log(4)

const first = () => (new Promise((resolve, reject) => {
    console.log(3);
    let p = new Promise((resolve, reject) => {
        console.log(7);
        setTimeout(() => {
            console.log(5);
            resolve(6);
        }, 0)
        resolve(1);
    });
    resolve(2);
    p.then((arg) => {
        console.log(arg);
    });

}));

first().then((arg) => {
    console.log(arg);
});
console.log(4);

Promise.resolve(1)
  .then((res) => {
    console.log(res)
    return 2
  })
  .catch((err) => {
    return 3
  })
  .then((res) => {
    console.log(res)
  })

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持续更新......