recursion await vs promise

main.js

function delay(t, v) {
    return new Promise(function(resolve) { 
        setTimeout(resolve.bind(null, v), t)
    });
 }

function f1(count = 10) {
    console.log('f1', count)
    let p = delay(10).then(() => {
        if (count > 0) {
            return f1(count - 1)
        } else {
            return count
        }
    })
    return p
}

async function f2(count = 10) {
    console.log('f2', count)
    await delay(10)
    if (count > 0) {
        return await f2(count - 1)
    } else {
        return count
    }
}

let r1 = f1()
r1.then((v)=>console.log('then1', v))

let r2 = f2()
r2.then((v)=>console.log('then2', v))

/*
f1 9 debugger eval code:8:5
f2 9 debugger eval code:20:5
f1 8 debugger eval code:8:5
f2 8 debugger eval code:20:5
f1 7 debugger eval code:8:5
f2 7 debugger eval code:20:5
f1 6 debugger eval code:8:5
f2 6 debugger eval code:20:5
f1 5 debugger eval code:8:5
f2 5 debugger eval code:20:5
f1 4 debugger eval code:8:5
f2 4 debugger eval code:20:5
f1 3 debugger eval code:8:5
f2 3 debugger eval code:20:5
f1 2 debugger eval code:8:5
f2 2 debugger eval code:20:5
f1 1 debugger eval code:8:5
f2 1 debugger eval code:20:5
f1 0 debugger eval code:8:5
f2 0 debugger eval code:20:5
then1 0 debugger eval code:30:14
then2 0 debugger eval code:33:14
*/