app-builder

import { compose } from 'app-builder'; // Define a simple logger middleware that logs entry and exit const loggerMiddleware = async (ctx, next) => { console.log(`Entering middleware: ${ctx.name}`); await next(); // This is crucial to pass control to the next middleware console.log(`Exiting middleware: ${ctx.name}`); }; // Define a core logic middleware that modifies the context const coreLogicMiddleware = async (ctx, next) => { ctx.data = 'Processed data'; console.log(`Core logic executed, data: ${ctx.data}`); await next(); }; // Define an error handling middleware to gracefully catch exceptions const errorHandlingMiddleware = async (ctx, next) => { try { await next(); } catch (error) { console.error(`An error occurred: ${error.message}`); ctx.error = error.message; // Store error in context } }; // Compose the middleware pipeline const app = compose( loggerMiddleware, // First, logs entry errorHandlingMiddleware, // Catches errors from subsequent middleware coreLogicMiddleware, // Performs core data processing async (ctx, next) => { // This is an inline middleware demonstrating further processing ctx.status = 'completed'; console.log(`Final status set to: ${ctx.status}`); await next(); // Even if it's the last, always call next() } ); // Define an initial context object const initialContext = { name: 'MyPipeline', data: null, status: null, error: null }; // Execute the pipeline app(initialContext) .then(() => { console.log('Pipeline finished. Final context:', initialContext); }) .catch(err => { console.error('Unhandled pipeline error (should not happen with errorHandlingMiddleware):', err); }); // Example with an intentional error to show error handling const failingApp = compose( errorHandlingMiddleware, // This will catch the error async (ctx, next) => { console.log('Failing middleware attempting to run...'); throw new Error('Something went wrong in the pipeline!'); } ); const failingContext = { name: 'FailingPipeline', error: null }; failingApp(failingContext) .then(() => { console.log('Failing pipeline finished. Final context:', failingContext); }) .catch(err => { console.error('Unhandled error in failing pipeline execution (should not happen):', err); });