Add event handler to upload files.

gistfile1.js

var bucketName = 'salesforce-bucket';
var bucket;
 
$(function() {
  initAWSCredentials();
  initEventHandlers();
  updateFileList();
});

function initAWSCredentials() {
  var assertion = $('#samlResponse').val();
  if (!assertion) {
    throw Error("No assertion is given to this page. Please access from app menu.");
  }
  AWS.config.credentials = new AWS.SAMLCredentials({
    RoleArn: 'arn:aws:iam::119301928242:role/SalesforceUserRole',
    PrincipalArn: 'arn:aws:iam::119301928242:saml-provider/SalesforceIdP',
    SAMLAssertion: assertion
  });
  bucket = new AWS.S3({ params: { Bucket: bucketName } });
}

function initEventHandlers() {
  $('#fileSelect').on('change', function() {
    uploadFile(this.files);
  });
}

function updateFileList() {
  bucket.listObjects({}, function(err, resp) {
    if (err) { throw err; }
    $('#fileList').empty();
    $.each(resp.Contents, function(i, content) {
      $('<li>').text(content.Key).appendTo($('#fileList'));
    });
  });
}

function uploadFile(files) {
  if (files && files.length > 0) {
    var file = files[0];
    var params = { Key: file.name, ContentType: file.type, Body: file };
    bucket.putObject(params, function(err, resp) {
       updateFileList();
    });
  }
}