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createModulePreloadMiddleware.mjs
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createModulePreloadMiddleware.mjs
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// @ts-check
import path from "node:path";
import resolveLinkRelations from "modulepreload-link-relations/resolveLinkRelations.mjs";
import formatLinkHeaderRelations from "modulepreload-link-relations/formatLinkHeaderRelations.mjs";
/** @typedef {import('express').RequestHandler} RequestHandler **/
const defaultOptions = {
extensions: ["mjs", "js"],
};
/**
* Creates a middleware function that adds a Link header containing modulepreload link relationships to JavaScript module requests.
* @param {string} appPath The relative path to the application root directory, eg "app".
* @param {Object} [userOptions] The options object.
* @param {Array<string>} [userOptions.extensions] The file extensions to consider for module scripts.
* @returns {RequestHandler} The middleware function.
*/
export default function createModulePreloadMiddleware(
appPath,
userOptions = {},
) {
const options = {
...defaultOptions,
...userOptions,
};
return async function modulePreloadMiddleware(req, res, next) {
const url = req.url;
const file = req.url?.slice(1);
const fileExt = file && path.extname(file).slice(1);
if (fileExt && options.extensions.includes(fileExt)) {
const linkRelations = await resolveLinkRelations({ appPath, url });
if (linkRelations) {
res.append("Link", formatLinkHeaderRelations(linkRelations));
}
}
next();
};
}