Chain promises with localforage

I am struggling with promises. I see how the chain of events is happening through .then().then().then().then().then().then().then().then().then().then().then().then() but I can not figure out how to make it end. I was hoping I could just make a simple :

 .then(callback(mydata))

However, I can't get that to work. I am trying to accomplish this.

function doSomethingCallback(theArrayComesBackHere) {
    theArrayComesBackHere.forEach(/*do stuff*/);
}    

button.onclick = () => {
   myobj.getlocalforagedata(doSomethingCallback);
}

myobj = {
   getlocalforagedata: (callback) => {
      var arr = [];
      localForage.keys().then((keys) => {
          keys.forEach((key) => {
              localForage.getItem(key).then(function (results) {
                  arr.push(results);
              });
          });
          callback && callback(arr);
      });
   }
}

Please help me break out of this madness.

The [previously] accepted answer to this question is using the explicit promise creation antipattern, a practice that makes code extra complicated and buggy.

You can accomplish what you are trying to do far more cleanly, like this:

function getLocalForageData() {
    return localForage.keys().then(function (keys) {
        return Promise.all(keys.map(function (key) {
            return localForage.getItem(key);
        });
    });
}

Example usage:

getLocalForageData()
    .then(function (values) {
        console.log(values);
    })
    .catch(function (error) {
        console.error(error);
    });

The above obtains an array of values, which are not matched up with their respective keys. If you would like the values paired with their keys, you can do this:

function getLocalForageData() {
    return localForage.keys().then(function (keys) {
        return Promise.all(keys.map(function (key) {
            return localForage.getItem(key)
                .then(function (value) {
                    return { key: key, value: value };
                });
        }));
    });
}

Or you could break out one of the inner functions to reduce the nesting:

function getLocalForageValueWithKey(key) {
    return localForage.getItem(key)
        .then(function (value) {
            return { key: key, value: value };
        });
}

function getLocalForageData() {
    return localForage.keys().then(function (keys) {
        return Promise.all(keys.map(getLocalForageValueWithKey));
    });
}

In either case, the code to call and use the getLocalForageData function would be the same as above.