Polyfill for ReadableStream.from in browser?

Question

ReadableStream.from for browsers is currently only supported in Firefox. I found the Node implementation in JavaScript, but it uses a lot of internal native node functions. Likewise, ReadableStream.from.toString() in Firefox's console reveals that its implementation is also a native function.

Is there a pure JavaScript implementation I can polyfill in temporarily? Perhaps using ReadableStreams constructor? I imagine the appropriate pull and cancel callbacks can be written based on the underlying iterator.

Answer 1

There is a ReadableStream polyfill on GitHub (https://github.com/MattiasBuelens/web-streams-polyfill) that includes a polyfill for ReadableStream.from:

const stream = ReadableStream.from(["Hello", "World!"]);
const reader = stream.getReader();

function process({ done, value }) {
    if(done) {
        console.log("(end of stream)");
        return;
    }
    console.log(value);
    reader.read().then(process);
};

reader.read().then(process);

<script src="https://unpkg.com/web-streams-polyfill/dist/polyfill.min.js"></script>