How to promisify a foreach loop

Question

I have this function:

remove(data.toString())
function remove(node){
    Item.findByIdAndDelete(node).then(()=>{
        Item.find({parent: mongoose.Types.ObjectId(node)}).select('_id').then((d)=>{
            d.forEach(e => {
                remove(e._id)
            });
        })
    })
}

I would like to promisify it so that I can call:

remove(data.toString()).then(()=>{console.log('done')})

how can I achieve this? any help would be greatly apprectiated!

Start by returning a promise from `remove`… then [stop using `forEach`](https://stackoverflow.com/a/37576787/1048572) — Bergi, Jul 13 '21 at 20:05

score 1 · Accepted Answer · answered Jul 13 '21 at 20:20

You should:

return each promise that is created in a callback.
map the array of promises that you get from the recursive calls (instead of forEach) and pass that array to Promise.all
flatten the promise chain, avoiding nested then callbacks.

function remove(node) {
    return Item.findByIdAndDelete(node).then(() => {
        return Item.find({parent: mongoose.Types.ObjectId(node)}).select('_id');
    }).then(d => {
        return Promise.all(d.map(e => {
            return remove(e._id)
        }));
    });
}

Things may become easier to read when using async await syntax:

async function remove(node) {
    await Item.findByIdAndDelete(node);
    let d = await Item.find({parent: mongoose.Types.ObjectId(node)}).select('_id');
    return Promise.all(d.map(e => remove(e._id)));
}

How to promisify a foreach loop

1 Answers1