前端复习之原型、事件循环

前言

网上收集的题目，供自己复习使用。

一、原型面试题

题目一

var A = function () {};
A.prototype.n = 1;
var b = new A();
A.prototype = {
  n: 2,
  m: 3,
};
var c = new A();

console.log(b.n);//1
console.log(b.m);//undefined

console.log(c.n);//2
console.log(c.m);//3

题目二

var F = function () {};

Object.prototype.a = function () {
  console.log("a");
};

Function.prototype.b = function () {
  console.log("b");
};

var f = new F();

f.a();//a
// f.b();//报错找不到函数

F.a();//a
F.b();//b

题目三

var foo = {},
F = function () {};
Object.prototype.a = "value a";
Function.prototype.b = "value b";

console.log(foo.a);//undefined
console.log(foo.b);//value b

console.log(F.a);//value a
console.log(F.b);//value b

二、事件循环

题目一

setTimeout(function () {
  console.log("setTimeout1");
  new Promise(function (resolve) {
    resolve();
  }).then(function () {
    new Promise(function (resolve) {
      resolve();
    }).then(function () {
      console.log("then4");
    });
    console.log("then2");
  });
});

new Promise(function (resolve) {
  console.log("promise1");
  resolve();
}).then(function () {
  console.log("then1");
});

setTimeout(function () {
  console.log("setTimeout2");
});

console.log(2);

queueMicrotask(() => {
  console.log("queueMicrotask1");
});

new Promise(function (resolve) {
  resolve();
}).then(function () {
  console.log("then3");
});
//promise1 2 then1 queueMicrotask1 then3 setTimeout1 then2 then4 setTimeout2

题目二

async function async1() {
  console.log("async1 start");
  await async2();
  console.log("async1 end");
}

async function async2() {
  console.log("async2");
}

console.log("script start");

setTimeout(function () {
  console.log("setTimeout");
}, 0);

async1();

new Promise(function (resolve) {
  console.log("promise1");
  resolve();
}).then(function () {
  console.log("promise2");
});

console.log("script end");

// script start
// async1 start
// async2
// promise1
// script end
// async1 end
// promise2
// setTimeout

题目三

console.log("script start");

async function async1() {
  await async2();
  console.log("async1 end");
}
async function async2() {
  console.log("async2 end");
}
async1();

setTimeout(function () {
  console.log("setTimeout");
}, 0);

new Promise((resolve) => {
  console.log("Promise");
  resolve();
})
  .then(function () {
    console.log("promise1");
  })
  .then(function () {
    console.log("promise2");
  });

console.log("script end");
//script start;async2 end;Promise;script end;async1 end;promise1;promise2;setTimeout

题目四

console.log("script start");

async function async1() {
  await async2();
  console.log("async1 end");
}
async function async2() {
  console.log("async2 end");
  return Promise.resolve().then(() => {
    console.log("async2 end1");
  });
}
async1();

setTimeout(function () {
  console.log("setTimeout");
}, 0);

new Promise((resolve) => {
  console.log("Promise");
  resolve();
})
  .then(function () {
    console.log("promise1");
  })
  .then(function () {
    console.log("promise2");
  });

console.log("script end");
//script start;async2 end;Promise;script end;promise1;promise2;async1 end;setTimeout