How to get content of a file in client script

In a suitelet page, we have a field(id: custpage_import_file) for uploading files(document field). The following script snippet shows how we can get the file object and get the file content.

var file = rec.getValue({
  fieldId: 'custpage_import_file'
});
if (file) {
      var fileDom = document.getElementsByName('custpage_import_items_field')[0].files;
      var fileObj = fileDom[0];
      var fileType = fileObj.type;
      var reader = new FileReader();
      // Read file into memory as UTF-8
      reader.readAsText(fileObj );
      // Handle errors load
      reader.onload = loadHandler;
      reader.onerror = errorHandler;
}

function loadHandler(event) {
    var fileContent= event.target.result;
  }

function errorHandler(evt) {
    if (evt.target.error.name == 'NotReadableError') {
      alert("Can't read file !");
    }
  }