Index

Fresh itself can be extended through the methods available on the App class or on the Builder class. Most of the features in Fresh itself are built using these APIs.

Custom middlewares

If you need to modify requests, add HTTP headers or pass additional data to other middlewares via ctx.state, then going with a middleware is the way to go.

const addXFreshHeader = define.middleware(async (ctx) => {
  const res = await ctx.next();
  res.headers.set("X-Fresh", "served by Fresh");
  return res;
});

Learn more about middlewares.

Creating reusable plugins

Since Fresh plugins are just middlewares and route handlers, creating a reusable plugin is as simple as exporting a function that returns a middleware:

import type { MiddlewareFn } from "fresh";

export function requestId(): MiddlewareFn<{ requestId: string }> {
  return async (ctx) => {
    ctx.state.requestId = crypto.randomUUID();
    const res = await ctx.next();
    res.headers.set("X-Request-Id", ctx.state.requestId);
    return res;
  };
}

import { App, staticFiles } from "fresh";
import { requestId } from "./plugins/request-id.ts";

const app = new App()
  .use(staticFiles())
  .use(requestId())
  .fsRoutes();

For more complex plugins, you can combine multiple middlewares, add routes, or use the Builder hooks for build-time processing.

Built-in plugins

Fresh ships with the following plugins:

• cors() - Set CORS HTTP headers
• csrf() - CSRF protection
• csp() - Content Security Policy headers
• trailingSlashes() - Enforce trailing slash behavior