file-worker

JavaScript File Worker

Process file asynchronously at Web Worker at browser.

Web Worker is a browser technology that allow some JavaScript code to be executed in the background, and very likely in another thread.

For example, if you want to compute the MD5 hash for a file at browser, the computation could take seconds depends on the size of the file, but you don't want the user interface to be frozen.

In this kind of situations, you can consider create a web worker for the job.

This package (file-worker) allows you to write file processing code easily that will be run in the background.

Usage

Step 1: Import the file

You can do it in HTML.

<script src="../../dist/browser/FileWorker.js"></script>

Or using NPM if you use webpack or TypeScript.

npm install file-worker --save-dev

Step 2: Write file processor

Assuming you want to compute the MD5 of your file, you can write a processor like this. However there is an existing library md5-webworker that does exactly the same thing.

function md5Processor(reader, writer) {
    reader.onData = function (bytes) {
        writer.write(computeMD5(bytes));
    };
    reader.readAll();
}

Writing a processor is very straight forward. It's a function that takes 2 parameters, one reader and one writer. However, please take now that this function is to be executed at the web worker, so you cannot access any variables or libraries directly inside the function. What you can do is to use the very handy importScripts function to load the script asynchronously.

Step 3: Get processed content

Assuming you get a File object from the browser's FileAPI. You can pass it to file worker, together with a type processor.

FileWorker.readFile(file, byteProcessor)
.then(function(result) {
    console.log(result);
});

FileWorker.readFile is an async function. You can either use .then and callback to get the result.