🔙 Backend Support

LiTScript supports now building server-side (backend) JS modules. These are request listener modules which the LiTScript development server loads, and reloads when its source changes. In a standalone deployment scenario, you include the built module in a node.js application. An example backend module can be found in tests/test-backend.ts.

import * as http from 'http'

Request Listener

The backend API is implemented as a single function reference whose type is RequestListener defined in the http module of node.js. We load the bundle dynamically and invalidate it whenever it's updated.

The full path to the bundled JS module is stored in the BackendModule object. The app contains the exported RequestListener, if it's loaded.

export interface BackendModule {
    path: string
    app?: http.RequestListener
}
let modules: BackendModule[] = []

Add a new the backend module to the list. If it's already there, unset the app reference and remove the bundle from Node.js require cache.

export function addOrUpdateBackendModule(path: string) {
    let mod = modules.find(m => m.path == path)
    if (mod) {
        mod.app = undefined
        delete require.cache[mod.path] 
    }
    else
        modules.push({ path })
}

This is the function that the development server calls to hanlde requests to backend. The backend is a bundled JS file whose default export should return the request listener callback. The callback can be asynchronous, and return a Promise. We must wait the promise to be resolved, if this is the case. Otherwise we might prematurely exit from the function before the request handler has completed.

export async function backend(req: http.IncomingMessage, 
    res: http.ServerResponse) {
    for (let i = 0; i < modules.length && !res.writableEnded; ++i) {
        let mod = modules[i]
        if (!mod.app)
            mod.app = require(mod.path).default
        await Promise.resolve(mod.app?.(req, res))
    }
}