encode-string-to-resizable-buffer.js

const TEXT_ENCODER = new TextEncoder();
const WASM_PAGE_SIZE = 1 << 16;

function encodeStringToBinary(str) {
  // Initially allocate enough space for the case where 1 char requires 1 byte (ASCII-only).
  let dest = new WebAssembly.Memory({ initial: Math.ceil(str.length / WASM_PAGE_SIZE) });
  let writePos = 0;

  for (;;) {
    // Write starting from the last written position.
    let { read, written } = TEXT_ENCODER.encodeInto(str, new Uint8Array(dest.buffer, writePos));
    // `read` is number of characters read from the string.
    // Slice them away to update the string to the leftover:
    str = str.slice(read);
    // If we don't have anything left, leave the loop:
    if (!str) break;
    // `write` is a number of bytes written to the output buffer.
    // First, update the write position:
    writePos += written;
    // Now, the only reason we are here is that there wasn't enough space in the output buffer.
    // This is where growable WebAssembly.Memory comes in handy!
    // Let's add one more page:
    dest.grow(1);
  }

  // If we're here, it means we've finally processed the whole string.
  // `writePos` contains the total number of bytes written, let's use it and return a view:
  return new Uint8Array(dest.buffer, 0, writePos);
}

var hugeRandomString = Array.from({ length: 1 << 20 }, () => String.fromCodePoint(0 | Math.random() * 0x110000)).join();
console.log(encodeStringToBinary(hugeRandomString));