学习js执行机制代码

涉及js event-loop,async await promise,宏微任务等等一些概念。

setTimeout(() => {
        console.log('setTimeout')
    }, 0)
    console.log('t1') 
    new Promise((resolve,reject)=>{
        setTimeout(() => {
            console.log(1);
            resolve(2);
        }, 0);
    })
        .then(function (response) {
            return new Promise((resolve)=>resolve(response));
        })
        .then(function (myJson) {
            console.log('myJson');
        })
        .catch(function (err) {
            console.log(err)
        })
    console.log('fetch zhi hou')
    async function async1() {
        console.log('async1 start') 
        await async2()
        console.log('async1 end') 
    }
    async1()
    console.log('t2') 
    new Promise((resolve) => {
        console.log('promise') 
        resolve()
    }).then(() => {
        console.log('promise.then')
    })
    console.log('t3') 
    async function async2() {
        console.log('async2') 
    }
    console.log('t4')
    ```