filereader-ponyfill

This package contains

• FileReaderAsync - a promisified edition of FileReader
• FileReaderSync - a porting of web worker's native FileReaderSync for main thread

Install

npm install import-ponyfill

Usage

FileReaderAsync

Sometimes you only need to use the load-error event of FileReader API and want to use promisified methods to fully read a file.

In short FileReaderAsync is to FileReader what fetch is to XMLHttpRequest

Example usage:

import {FileReaderAsync} from 'filereader-ponyfill';
// import FileReaderAsync from 'filereader-ponyfill/src/FileReaderAsync.js'; // ESM
// import FileReaderAsync from 'filereader-ponyfill/dist/FileReaderAsync.js'; // UMD

new FileReaderAsync().readAsText(file).then((text)=> {

}, (error)=> {

});

// or
try {
  let text = await new FileReaderAsync().readAsText(file);
} catch (error) {

}

FileReaderSync for main thread

In some extreme situations you may want to read a file synchronously, native FileReaderSync can do that but is only available in Web Worker.

This FileReaderSync is designed for main thread and implemented behaviors of web worker's native FileReaderSync.

Example usage:

import {FileReaderSync} from 'filereader-ponyfill';
// import FileReaderSync from 'filereader-ponyfill/src/FileReaderSync.js'; // ESM
// import FileReaderSync from 'filereader-ponyfill/dist/FileReaderSync.js'; // UMD

try {
  let text = new FileReaderSync().readAsText(file);
} catch (error) {

}

Implementation notes:

[ blob ] ------> URL.createObjectURL ------> [ blobUrl ]
                                                       |
[ binaryString ] <------> sync XMLHttpRequest <------
|
------> TextDecoder / btoa / ... ------> [ finalData ]