ES6 -async ,await

async function fn(){
    return 123;
}
console.log(fn());//返回promise对象，Promise {<resolved>: 123}

// 获取return值
fn().then(res=>{
    console.log(res);//123
})

// 只要await语句后面Promise状态变成reject,那么整个async函数中断执行
async function fn(){
    await Promise.reject(‘fail‘);
   let a=await Promise.resolve(‘success‘);
   console.log(a);
}


fn().then(res=>{
    console.log(res);
}).catch(err=>{
    console.log(err);//fail
})

// 1.try catch :
async function fn(){
    try{
        await Promise.reject(‘fail‘);
    }catch(e){

    }
   let a=await Promise.resolve(‘success‘);
   console.log(a);//success
   return 123;
}

fn().then(res=>{
    console.log(res);//123
}).catch(err=>{
    console.log(err);
})

// 2.promise 本身catch

async function fn(){
    await Promise.reject(‘fail‘).catch(err=>{
        console.log(err);//fail
    })
   let a=await Promise.resolve(‘success‘);
   console.log(a);//success
   return 123;
}

fn().then(res=>{
    console.log(res);//123
}).catch(err=>{
    console.log(err);
})