nstdlib-nightly/lib/internal/modules/esm/formats.mjs

Node.js standard library converted to runtime-agnostic ES modules.

// Source: https://github.com/nodejs/node/blob/65eff1eb/lib/internal/modules/esm/formats.js

import { getOptionValue } from "nstdlib/lib/internal/options";
import { getValidatedPath } from "nstdlib/lib/internal/fs/utils";
import * as fsBindings from "nstdlib/stub/binding/fs";
import { fs as fsConstants } from "nstdlib/stub/binding/constants";

const experimentalWasmModules = getOptionValue("--experimental-wasm-modules");

const extensionFormatMap = {
  __proto__: null,
  ".cjs": "commonjs",
  ".js": "module",
  ".json": "json",
  ".mjs": "module",
};

if (experimentalWasmModules) {
  extensionFormatMap[".wasm"] = "wasm";
}

if (getOptionValue("--experimental-strip-types")) {
  extensionFormatMap[".ts"] = "module-typescript";
  extensionFormatMap[".mts"] = "module-typescript";
  extensionFormatMap[".cts"] = "commonjs-typescript";
}

/**
 * @param {string} mime
 * @returns {string | null}
 */
function mimeToFormat(mime) {
  if (
    RegExp.prototype.exec.call(
      /^\s*(text|application)\/javascript\s*(;\s*charset=utf-?8\s*)?$/i,
      mime,
    ) !== null
  ) {
    return "module";
  }
  if (mime === "application/json") {
    return "json";
  }
  if (experimentalWasmModules && mime === "application/wasm") {
    return "wasm";
  }
  return null;
}

/**
 * For extensionless files in a `module` package scope, or a default `module` scope enabled by the
 * `--experimental-default-type` flag, we check the file contents to disambiguate between ES module JavaScript and Wasm.
 * We do this by taking advantage of the fact that all Wasm files start with the header `0x00 0x61 0x73 0x6d` (`_asm`).
 * @param {URL} url
 */
function getFormatOfExtensionlessFile(url) {
  if (!experimentalWasmModules) {
    return "module";
  }
  const path = getValidatedPath(url);
  switch (fsBindings.getFormatOfExtensionlessFile(path)) {
    case fsConstants.EXTENSIONLESS_FORMAT_WASM:
      return "wasm";
    default:
      return "module";
  }
}

export { extensionFormatMap };
export { getFormatOfExtensionlessFile };
export { mimeToFormat };