Promise resolve issue

Question

I am trying read list of files stored in zip file and parse it according to the requirement.

zip Structure

folder 1 -> file1.json

folder 2 -> file2.json

to an object

{
  folder1: {file1: {file1json Data}},
  folder2: {file2: {file1json Data}}
}

How to wait in

lis.reduce till 
return oFileReader.readFile(new File([current[1]], path[1]))
.then(oResult => { 
     accumulator[path[0]].data = oResult
})

returns result and store it in accumulator object

readZipFile: function(oFile) {
    return new Promise(function(resolve, reject) {
        return JSZip.loadAsync(oFile).then(function(zip) {
            var entries = Object.keys(zip.files).map(function(name) {
                return zip.files[name];
            });
            var listOfPromises = entries.map(function(entry) {
                return entry.async("blob").then(function(data) {
                    return [entry.name, data];
                });
            });
            var promiseOfList = Promise.all(listOfPromises);
            promiseOfList.then(function(list) {
                var result = list.reduce(function(accumulator, current) {
                    let currentName = current[0];
                    let path = currentName.split("/");

                    if (currentName.includes('.json')) {
                        let oFileReader = new new FileReader();
                        return oFileReader.readFile(new File([current[1]], path[1]))
                            .then(oResult => {
                                accumulator[path[0]].data = oResult
                            })
                    }
                    return accumulator;
                }, {});
                resolve(result);
            });
        });
    }.bind(this));
},