# koa-convert > convert modern Koa legacy generator-based middleware to promise-based middleware Latest version **2.0.0** (published 2020-09-10) · MIT license · 0 weekly downloads ## Install ```sh npm install koa-convert pnpm add koa-convert yarn add koa-convert bun add koa-convert ``` ## Health **Score 23/100 (F)** — status: abandoned. Positive: has types package; no vulnerabilities; high quality score. Warnings: low downloads; no esm support. Negative: abandoned; low maintenance score. ## Facts | | | |---|---| | Version | 2.0.0 | | Published | 2020-09-10 | | First published | 2015-10-11 | | Weekly downloads | 0 | | License | MIT | | TypeScript types | separate (@types/koa-convert) | | Module format | CommonJS | | Node | >= 10 | | Dependencies | 2 | | Unpacked size | 9 KB | | Known vulnerabilities | 0 | | Install scripts | no | | GitHub stars | 251 | | Author | gyson | | Maintainers | gyson, niftylettuce | | Keywords | koa, middleware, convert, back, generator, promise, generator-based-middleware, promise-based-middleware, support | ## Links - npm: https://www.npmjs.com/package/koa-convert - Repository: https://github.com/gyson/koa-convert - Homepage: https://github.com/gyson/koa-convert#readme - Issues: https://github.com/gyson/koa-convert/issues - npm.io page: https://npm.io/package/koa-convert ## Dependencies (2) - [co](https://npm.io/package/co.md) ^4.6.0 - [koa-compose](https://npm.io/package/koa-compose.md) ^4.1.0 ## Alternatives - [@sindresorhus/slugify](https://npm.io/package/@sindresorhus/slugify.md) — 3.7M weekly downloads - [solid-js](https://npm.io/package/solid-js.md) — 2.7M weekly downloads - [expo-glass-effect](https://npm.io/package/expo-glass-effect.md) — 2.5M weekly downloads - [nanoassert](https://npm.io/package/nanoassert.md) — 780.8K weekly downloads - [@ffmpeg/ffmpeg](https://npm.io/package/@ffmpeg/ffmpeg.md) — 529.5K weekly downloads ## Recent versions - 2.0.0 (latest) — 2020-09-10 - 1.2.0 — 2015-11-16 - 1.1.0 — 2015-11-06 - 1.0.0 — 2015-11-01 - 0.0.2 — 2015-10-11 - 0.0.1 — 2015-10-11 ## README # koa-convert [![Build Status][travis-img]][travis-url] [![NPM version][npm-badge]][npm-url] [![License][license-badge]][license-url] ![Code Size][code-size-badge] [travis-img]: https://travis-ci.org/koajs/convert.svg?branch=master [travis-url]: https://travis-ci.org/koajs/convert [npm-badge]: https://img.shields.io/npm/v/koa-better-request-id.svg?style=flat [npm-url]: https://www.npmjs.com/package/koa-better-request-id [license-badge]: https://img.shields.io/badge/license-MIT-green.svg?style=flat-square [license-url]: https://github.com/koajs/koa-convert/blob/master/LICENSE [code-size-badge]: https://img.shields.io/github/languages/code-size/koajs/koa-convert Convert Koa legacy (0.x & 1.x) generator middleware to modern promise middleware (2.x). It could also convert modern promise middleware back to legacy generator middleware (useful to help modern middleware support Koa v0.x or v1.x). ## Note Router middleware is special case here. Because it reimplements middleware composition internally, we cannot not simply convert it. You may use following packages for [routing](https://github.com/koajs/koa/wiki#routing-and-mounting), which are koa 2.x ready now: * [koa-route@3.0.0](https://github.com/koajs/route/tree/next) * [koa-simple-router](https://github.com/gyson/koa-simple-router) * [koa-router@next](https://github.com/alexmingoia/koa-router/tree/master) * [koa-66](https://github.com/menems/koa-66) ## Installation ```bash # npm .. $ npm i koa-convert # yarn .. $ yarn add koa-convert ``` ## Usage ```js const Koa = require('koa') // koa v2.x const convert = require('koa-convert') const app = new Koa() app.use(modernMiddleware) app.use(convert(legacyMiddleware)) app.use(convert.compose(legacyMiddleware, modernMiddleware)) function * legacyMiddleware (next) { // before yield next // after } function modernMiddleware (ctx, next) { // before return next().then(() => { // after }) } ``` ## Distinguish legacy and modern middleware In koa 0.x and 1.x (without experimental flag), `app.use` has an assertion that all (legacy) middleware must be generator function and it's tested with `fn.constructor.name == 'GeneratorFunction'` at [here](https://github.com/koajs/koa/blob/7fe29d92f1e826d9ce36029e1b9263b94cba8a7c/lib/application.js#L105). Therefore, we can distinguish legacy and modern middleware with `fn.constructor.name == 'GeneratorFunction'`. ## Migration `app.use(legacyMiddleware)` is everywhere in 0.x and 1.x and it would be painful to manually change all of them to `app.use(convert(legacyMiddleware))`. You can use following snippet to make migration easier. ```js const _use = app.use app.use = x => _use.call(app, convert(x)) ``` The above snippet will override `app.use` method and implicitly convert all legacy generator middleware to modern promise middleware. Therefore, you can have both `app.use(modernMiddleware)` and `app.use(legacyMiddleware)` and your 0.x or 1.x should work without modification. Complete example: ```js const Koa = require('koa') // v2.x const convert = require('koa-convert') const app = new Koa() // ---------- override app.use method ---------- const _use = app.use app.use = x => _use.call(app, convert(x)) // ---------- end ---------- app.use(modernMiddleware) // this will be converted to modern promise middleware implicitly app.use(legacyMiddleware) function * legacyMiddleware (next) { // before yield next // after } function modernMiddleware (ctx, next) { // before return next().then(() => { // after }) } ``` ## API #### `convert()` Convert legacy generator middleware to modern promise middleware. ```js modernMiddleware = convert(legacyMiddleware) ``` #### `convert.compose()` Convert and compose multiple middleware (could mix legacy and modern ones) and return modern promise middleware. ```js composedModernMiddleware = convert.compose(legacyMiddleware, modernMiddleware) // or composedModernMiddleware = convert.compose([legacyMiddleware, modernMiddleware]) ``` #### `convert.back()` Convert modern promise middleware back to legacy generator middleware. This is useful to help modern promise middleware support koa 0.x or 1.x. ```js legacyMiddleware = convert.back(modernMiddleware) ``` ## License [MIT](LICENSE) --- _Source: https://npm.io/package/koa-convert · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._