promise

function a() {
    return new Promise(resolve => {
        setTimeout(() => {
            console.log('A')
            resolve()
        }, 1000);
    })
}
 
async function test2017() {
    await a()
    console.log('B')
}
 
function test2015() {
    a().then(() => {
        console.log('B')
    })
}
 
test2017()
test2015()