const promiseA = Promise.resolve('a')
promiseA.then((res) => {
console.log(res)
}).then((res) => {
console.log(res)
})
const promiseB = Promise.resolve('b')
promiseB.then((res) => {
console.log(res)
})
promiseB.then((res) => {
console.log(res)
})
a b b undefined
a undefined b b
a b undefined undefined
a b a b