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137 lines
3.4 KiB
Markdown
137 lines
3.4 KiB
Markdown
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# koa-convert
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[](https://npmjs.org/package/koa-convert)
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[](https://travis-ci.org/gyson/koa-convert)
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Convert koa legacy ( 0.x & 1.x ) generator middleware to modern promise middleware ( 2.x ).
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It could also convert modern promise middleware back to legacy generator middleware ( useful to help modern middleware support koa 0.x or 1.x ).
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## Note
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It should be able to convert any legacy generator middleware to modern promise middleware ( or convert it back ).
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Please let me know ( send a issue ) if you fail to do so.
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## Installation
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```
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$ npm install koa-convert
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```
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## Usage
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```js
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const Koa = require('koa') // koa v2.x
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const convert = require('koa-convert')
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const app = new Koa()
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app.use(modernMiddleware)
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app.use(convert(legacyMiddleware))
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app.use(convert.compose(legacyMiddleware, modernMiddleware))
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function * legacyMiddleware (next) {
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// before
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yield next
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// after
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}
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function modernMiddleware (ctx, next) {
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// before
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return next().then(() => {
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// after
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})
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}
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```
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## Distinguish legacy and modern middleware
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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).
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Therefore, we can distinguish legacy and modern middleware with `fn.constructor.name == 'GeneratorFunction'`.
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## Migration
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`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))`.
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You can use following snippet to make migration easier.
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```js
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const _use = app.use
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app.use = x => _use.call(app, convert(x))
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```
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The above snippet will override `app.use` method and implicitly convert all legacy generator middleware to modern promise middleware.
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Therefore, you can have both `app.use(modernMiddleware)` and `app.use(legacyMiddleware)` and your 0.x or 1.x should work without modification.
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Complete example:
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```js
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const Koa = require('koa') // v2.x
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const convert = require('koa-convert')
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const app = new Koa()
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// ---------- override app.use method ----------
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const _use = app.use
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app.use = x => _use.call(app, convert(x))
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// ---------- end ----------
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app.use(modernMiddleware)
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// this will be converted to modern promise middleware implicitly
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app.use(legacyMiddleware)
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function * legacyMiddleware (next) {
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// before
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yield next
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// after
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}
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function modernMiddleware (ctx, next) {
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// before
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return next().then(() => {
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// after
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})
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}
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```
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## API
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#### `convert()`
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Convert legacy generator middleware to modern promise middleware.
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```js
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modernMiddleware = convert(legacyMiddleware)
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```
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#### `convert.compose()`
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Convert and compose multiple middleware (could mix legacy and modern ones) and return modern promise middleware.
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```js
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composedModernMiddleware = convert.compose(legacyMiddleware, modernMiddleware)
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// or
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composedModernMiddleware = convert.compose([legacyMiddleware, modernMiddleware])
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```
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#### `convert.back()`
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Convert modern promise middleware back to legacy generator middleware.
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This is useful to help modern promise middleware support koa 0.x or 1.x.
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```js
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legacyMiddleware = convert.back(modernMiddleware)
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```
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## License
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MIT
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