2021-03-04

js

判断执行顺序

async function async1() {
  console.log("async1 start"); //2
  await async2();
  console.log("asnyc1 end"); //6
}
 function async2() {
  console.log("async2"); //3
}
console.log("script start");  //1
setTimeout(() => {
  console.log("setTimeOut"); //8
}, 0);
async1();
new Promise(function (reslove) {
  console.log("promise1");  //4
  reslove();
}).then(function () {
  console.log("promise2");  //7
});
console.log("script end"); //5

手动编写new方法

function AA(name, age) {
  this.name = name;
  this.age = age;
}

function myNew(Fn, ...arg) {
  let obj = Object.create(Fn.prototype);
  Fn.apply(obj, arg);
  return obj;
}
console.log(myNew(AA, "aa", 30));  //AA {name: "aa", age: 30}

为什么输出函数

var b = 10;
(function b() {
  b = 20;
  console.log(b);
})();

首先进行变量提升b，然后执行自定义函数，里面的b = 20没有使用var，所以是全局window下的属性，打印时会从里向外找，会首先找到函数b