Wait for forEach with a promise inside to finish

Instead of forEach() use map() to create an array of promises and then use Promise.all()

let promiseArr = arr.map(function (resource) {
    // return the promise to array
    return someModule.someFunction(resource).then(function (res) { //a Promise
        //do something with the resource that has been modified with someFunction
        return res;
    })
});

Promise.all(promiseArr).then(function(resultsArray){
   // do something after the loop finishes
}).catch(function(err){
   // do something when any of the promises in array are rejected
})