将函数传递给 Promise ES6

Question

I've seen questions similar to this in various forms but I can't seem to crack this particular case...

I want to pass a function inside a Promise, then execute that Promise and do something with the result. The function to be passed in is the database transaction txn function below:

db.transaction(txn => {
    //lodash reduce function to execute each promise sequentially
    _.reduce(promisesToExecute, (pending, next, i) => {
        return next
           //this bit is wrong but I don't know how else to pass in txn
           //how should I pass txn into the promise?
           .then(fn => fn(txn))
           .then(newIds => {
               if (newIds) {
                   returnContent[i] = newIds
               }
               return next
           })
    }, Promise.resolve())
})

And the promise I want to execute is here

 (newVals, id, fkId) => {
        return new Promise((resolve, reject) => {
            return txn => {
                //I want txn to be available in here to use
                return db.table('Users')
                    .insert(newVals)
                    .transacting(txn)
                    .then(res => {
                        resolve(res.id)
                    })
                    .catch(err => {
                        reject(err)
                    })
        }
    })

Any ideas? Do I need to somehow pass the newIds => {} function in as a callback?

Answer 1

The problem here is that you're creating promises that will never resolve. They have a function inside them that never gets called, and the resolve and reject hang off of that function.

So fix your second chunk of code to return functions, not promises:

(newVals, id, fkId) =>
    txn => 
        db.table('Users')
            .insert(newVals)
            .transacting(txn)
            .then(res => res.id)

Then fix the first chunk of code accordingly:

db.transaction(txn =>
    _.reduce(functions, (pending, next, i) =>
        next(txn)
           .then(newIds => {
               if (newIds) {
                   returnContent[i] = newIds
               }
           })
    , Promise.resolve())
);