p.js

const f = (id, fail) =>
    new Promise((y, n) =>
        setTimeout(_ => {
            console.log(id)
            fail ? n() : y()
        }, 100)
    )

const a = _ =>
    new Promise(y =>
        f('a1')
        .then(_ => f('a2'))
        .then(_ => f('a3'))
        .then(y)
        .catch(y)
    )

const b = _ =>
    new Promise(y =>
        f('b1', 1)
        .then(_ => f('b2'))
        .then(_ => f('b3'))
        .then(y)
        .catch(y)
    )

const c = _ =>
    new Promise(y =>
        f('c1')
        .then(_ => f('c2', 1))
        .then(_ => f('c3'))
        .then(y)
        .catch(y)
    )

{
    a()
    .then(b)
    .then(c)
    .then(_ => console.log("success"))
    .catch(_ => console.log("unreachable"))
}

p.out

a1
a2
a3
b1
c1
c2
success