Converting Blob To ArrayBuffer Will Not Work

I am trying to convert a blob to an array. The blob has a .size that is not zero and after the assignment of this.result which should give the converted array is zero length. Can anybody help?

function createArrayFromBlob(blob){
    return new Promise(function(resolve, reject) {
        var arrayBuffer;
        var fileReader = new FileReader();
        fileReader.onload = function() {
            console.log("3: " + blob.size);

            arrayBuffer = this.result;

            console.log("4: " + arrayBuffer.length);

            resolve(arrayBuffer);
        };

        fileReader.onerror = function(e) {
            console.log(e);
        };

        fileReader.readAsArrayBuffer(blob);
    });
}

Output:

3: 4196020
4: undefined