134 lines
3.9 KiB
Markdown
134 lines
3.9 KiB
Markdown
# Migrating from Koa v1.x to v2.x
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## New middleware signature
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Koa v2 introduces a new signature for middleware.
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**Old signature middleware (v1.x) support will be removed in v3**
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The new middleware signature is:
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```js
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// uses async arrow functions
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app.use(async (ctx, next) => {
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try {
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await next() // next is now a function
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} catch (err) {
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ctx.body = { message: err.message }
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ctx.status = err.status || 500
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}
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})
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app.use(async ctx => {
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const user = await User.getById(this.session.userid) // await instead of yield
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ctx.body = user // ctx instead of this
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})
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```
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You don't have to use asynchronous functions - you just have to pass a function that returns a promise.
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A regular function that returns a promise works too!
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The signature has changed to pass `Context` via an explicit parameter, `ctx` above, instead of via
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`this`. The context passing change makes Koa more compatible with es6 arrow functions, which capture `this`.
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## Using v1.x Middleware in v2.x
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Koa v2.x will try to convert legacy signature, generator middleware on `app.use`, using [koa-convert](https://github.com/koajs/convert).
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It is however recommended that you choose to migrate all v1.x middleware as soon as possible.
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```js
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// Koa will convert
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app.use(function *(next) {
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const start = Date.now();
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yield next;
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const ms = Date.now() - start;
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console.log(`${this.method} ${this.url} - ${ms}ms`);
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});
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```
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You could do it manually as well, in which case Koa will not convert.
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```js
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const convert = require('koa-convert');
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app.use(convert(function *(next) {
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const start = Date.now();
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yield next;
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const ms = Date.now() - start;
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console.log(`${this.method} ${this.url} - ${ms}ms`);
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}));
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```
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## Upgrading middleware
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You will have to convert your generators to async functions with the new middleware signature:
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```js
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app.use(async (ctx, next) => {
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const user = await Users.getById(this.session.user_id);
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await next();
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ctx.body = { message: 'some message' };
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})
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```
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Upgrading your middleware may require some work. One migration path is to update them one-by-one.
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1. Wrap all your current middleware in `koa-convert`
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2. Test
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3. `npm outdated` to see which Koa middleware is outdated
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4. Update one outdated middleware, remove using `koa-convert`
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5. Test
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6. Repeat steps 3-5 until you're done
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## Updating your code
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You should start refactoring your code now to ease migrating to Koa v2:
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- Return promises everywhere!
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- Do not use `yield*`
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- Do not use `yield {}` or `yield []`.
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- Convert `yield []` into `yield Promise.all([])`
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- Convert `yield {}` into `yield Bluebird.props({})`
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You could also refactor your logic outside of Koa middleware functions. Create functions like
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`function* someLogic(ctx) {}` and call it in your middleware as
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`const result = yield someLogic(this)`.
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Not using `this` will help migrations to the new middleware signature, which does not use `this`.
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## Application object constructor requires new
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In v1.x, the Application constructor function could be called directly, without `new` to
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instantiate an instance of an application. For example:
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```js
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var koa = require('koa');
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var app = module.exports = koa();
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```
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v2.x uses es6 classes which require the `new` keyword to be used.
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```js
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var koa = require('koa');
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var app = module.exports = new koa();
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```
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## ENV specific logging behavior removed
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An explicit check for the `test` environment was removed from error handling.
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## Dependency changes
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- [co](https://github.com/tj/co) is no longer bundled with Koa. Require or import it directly.
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- [composition](https://github.com/thenables/composition) is no longer used and deprecated.
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## v1.x support
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The v1.x branch is still supported but should not receive feature updates. Except for this migration
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guide, documentation will target the latest version.
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## Help out
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If you encounter migration related issues not covered by this migration guide, please consider
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submitting a documentation pull request.
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