web-worker-helper/src/utils/worker-utils/get-transfer-list.ts

Utilities for running tasks on worker threads

// NOTE - there is a copy of this function is both in core and loader-utils
// core does not need all the utils in loader-utils, just this one.

/**
 * Returns an array of Transferrable objects that can be used with postMessage
 * https://developer.mozilla.org/en-US/docs/Web/API/Worker/postMessage
 * @param object data to be sent via postMessage
 * @param recursive - not for application use
 * @param transfers - not for application use
 * @returns a transfer list that can be passed to postMessage
 */
export function getTransferList(object: any, recursive = true, transfers?: Set<any>): Transferable[] {
  // Make sure that items in the transfer list is unique
  const transfersSet = transfers || new Set();

  if (!object) {
    // ignore
  } else if (isTransferable(object)) {
    transfersSet.add(object);
  } else if (isTransferable(object.buffer)) {
    // Typed array
    transfersSet.add(object.buffer);
  } else if (ArrayBuffer.isView(object)) {
    // object is a TypeArray viewing into a SharedArrayBuffer (not transferable)
    // Do not iterate through the content in this case
  } else if (recursive && typeof object === 'object') {
    for (const key in object) {
      // Avoid perf hit - only go one level deep
      getTransferList(object[key], recursive, transfersSet);
    }
  }

  // If transfers is defined, is internal recursive call
  // Otherwise it's called by the user
  return transfers === undefined ? Array.from(transfersSet) : [];
}

// https://developer.mozilla.org/en-US/docs/Web/API/Transferable
function isTransferable(object: unknown) {
  if (!object) {
    return false;
  }
  if (object instanceof ArrayBuffer) {
    return true;
  }
  if (typeof MessagePort !== 'undefined' && object instanceof MessagePort) {
    return true;
  }
  if (typeof ImageBitmap !== 'undefined' && object instanceof ImageBitmap) {
    return true;
  }
  // eslint-disable-next-line @typescript-eslint/ban-ts-comment
  // @ts-ignore
  if (typeof OffscreenCanvas !== 'undefined' && object instanceof OffscreenCanvas) {
    return true;
  }
  return false;
}