Chaining multiple promises

Sometimes we need to perform several asynchronous operations, no matter the order, and to be notified when they all done.
$q.all(promisesArr) can help us with that.
Assume we have N methods that return promises: async1(), ..., asyncN().
The following code will log done only when all operations are resolved successfully.

function readOneFileAsDataURL (file, scope) {
    var deferred = $q.defer();
    var reader = getReader(deferred, scope);         
    reader.readAsDataURL(file);
    return deferred.promise;
};
function readManyFileAsDataURL (files, scope){
    var promises=[];
    for(var i = 0 ; i < files.length; i ++){
        promises.push(readOneFileAsDataURL(files[i], scope));
    }
    return $q.all(promises);
};
/*
*Usage 
*/
readManyFileAsDataURL(files, scope).then(function(allImages){
    console.log(allImages.length);
});

Result:

/*
*Some log for more clear
"begin read image : 0"
"begin read image : 1"
"begin read image : 2"
"end read image : 2"
"end read image : 0"
"end read image : 1"
*
/