excalidraw/packages/excalidraw/subset/harfbuzz/harfbuzz-loader.ts

/**
 * DON'T depend on anything from the outside like `promiseTry`, as this module is part of a separate lazy-loaded chunk.
 *
 * Including anything from the main chunk would include the whole chunk by default.
 * Even it it would be tree-shaken during build, it won't be tree-shaken in dev.
 *
 * In the future consider separating common utils into a separate shared chunk.
 */

import bindings from "./harfbuzz-bindings";
import binary from "./harfbuzz-wasm";

/**
 * Lazy loads wasm and respective bindings for font subsetting based on the harfbuzzjs.
 */
let loadedWasm: ReturnType<typeof load> | null = null;

// TODO: consider adding support for fetching the wasm from an URL (external CDN, data URL, etc.)
const load = (): Promise<{
  subset: (
    fontBuffer: ArrayBuffer,
    codePoints: ReadonlySet<number>,
  ) => Uint8Array<ArrayBuffer>;
}> => {
  return new Promise(async (resolve, reject) => {
    try {
      const module = await WebAssembly.instantiate(binary);
      const harfbuzzJsWasm = module.instance.exports;
      // @ts-expect-error since `.buffer` is custom prop
      const heapu8 = new Uint8Array(harfbuzzJsWasm.memory.buffer);

      const hbSubset = {
        subset: (fontBuffer: ArrayBuffer, codePoints: ReadonlySet<number>) => {
          return bindings.subset(
            harfbuzzJsWasm,
            heapu8,
            fontBuffer,
            codePoints,
          );
        },
      };

      resolve(hbSubset);
    } catch (e) {
      reject(e);
    }
  });
};

// lazy load the default export
export default (): ReturnType<typeof load> => {
  if (!loadedWasm) {
    loadedWasm = load();
  }

  return loadedWasm;
};