webpack/lib/loaders/loadLoader.js

Packs ECMAScript/CommonJs/AMD modules for the browser. Allows you to split your codebase into multiple bundles, which can be loaded on demand. Supports loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/

"use strict";

const { pathToFileURL } = require("url");
const LoaderLoadingError = require("../errors/LoaderLoadingError");

/** @typedef {import("./LoaderRunner").LoaderObject} LoaderObject */

/**
 * Lazily-compiled dynamic `import()`. Built on first use so this file still
 * parses on Node versions without native `import()` (<13.2), then reused.
 * @type {((url: URL) => Promise<EXPECTED_ANY>) | undefined}
 */
let importModule;

/**
 * @param {LoaderObject} loader the loader to load into
 * @param {EXPECTED_ANY} module the loaded module
 * @param {(err?: Error) => void} callback callback
 * @returns {void}
 */
function handleResult(loader, module, callback) {
	if (typeof module !== "function" && typeof module !== "object") {
		return callback(
			new LoaderLoadingError(
				`Module '${loader.path}' is not a loader (export function or es6 module)`
			)
		);
	}

	loader.normal = typeof module === "function" ? module : module.default;
	loader.pitch = module.pitch;
	loader.raw = module.raw;

	if (
		typeof loader.normal !== "function" &&
		typeof loader.pitch !== "function"
	) {
		return callback(
			new LoaderLoadingError(
				`Module '${loader.path}' is not a loader (must have normal or pitch function)`
			)
		);
	}
	callback();
}

/**
 * @param {LoaderObject} loader the loader to load
 * @param {(err?: Error) => void} callback callback
 * @returns {void}
 */
function loadLoader(loader, callback) {
	if (loader.type === "module") {
		try {
			if (importModule === undefined) {
				// `eval` defers parsing `import()` to runtime, so this file stays
				// loadable on Node versions that can't parse it (<13.2).
				// eslint-disable-next-line no-eval
				const dynamicImport = eval("(url) => import(url)");
				importModule = /** @type {(url: URL) => Promise<EXPECTED_ANY>} */ (
					dynamicImport
				);
			}

			importModule(pathToFileURL(loader.path)).then(
				(/** @type {EXPECTED_ANY} */ module) => {
					handleResult(loader, module, callback);
				},
				callback
			);
		} catch (err) {
			callback(/** @type {Error} */ (err));
		}
		return;
	}

	let loadedModule;
	try {
		loadedModule = require(loader.path);
	} catch (err) {
		// node can choke on require when the FD limit is hit; defer to recover.
		if (
			err instanceof Error &&
			/** @type {NodeJS.ErrnoException} */ (err).code === "EMFILE"
		) {
			setImmediate(loadLoader, loader, callback);
			return;
		}
		return callback(/** @type {Error} */ (err));
	}

	return handleResult(loader, loadedModule, callback);
}

module.exports = loadLoader;