@patternfly/react-core/src/helpers/fileUtils.ts

This library provides a set of common React components for use with the PatternFly reference implementation.

export enum fileReaderType {
  text = 'text',
  dataURL = 'dataURL'
}

/**
 * Read a file using the FileReader API, either as a plain text string or as a DataURL string.
 * Returns a promise which will resolve with the file contents as a string or reject with a DOMException.
 *
 * @param {File} fileHandle - File object to read
 * @param {fileReaderType} type - How to read it
 */
export function readFile(fileHandle: File, type: fileReaderType) {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = () => resolve(reader.result);
    reader.onerror = () => reject(reader.error);
    if (type === fileReaderType.text) {
      reader.readAsText(fileHandle);
    } else if (type === fileReaderType.dataURL) {
      reader.readAsDataURL(fileHandle);
    } else {
      reject('unknown type');
    }
  });
}