vamsiampolu vamsiampolu - 3 months ago 30
Javascript Question

Error composing koa async function middleware

I am using

koa-compose
to put together middleware as suggested in the guide. I import
koa-compose
as
kompose
.

I have the following code:

const home = async function home (ctx,next) {
if(ctx.path === '/') {
ctx.body = 'Hello World!'
} else {
await next()
}
}

const random = async function random (ctx,next) {
console.log(ctx)
if(ctx.path === '/random') {
console.log('Inside random function')
ctx.body = Math.floor(Math.random() * 10)
} else {
await next()
}
}

const backwards = async function backwards (ctx,next) {
if(ctx.path === '/backwards') {
ctx.body = 'sdrawkcab'
} else {
await next()
}
}

const pi = async function pi (ctx,next) {
if(ctx.path === '/pi') {
ctx.body = String(Math.PI)
} else {
await next()
}
}

const body2 = kompose([random,backwards,pi,home])


I use it as the last middleware in the chain:

app.use(responseTime())
app.use(logger())
app.use(body2)
app.listen(3000)


I get this error:

TypeError: undefined is not a function
at Object.<anonymous> (/home/vamsi/Do/koa-tutorial/node_modules/koa-compose/index.js:28:19)
at undefined.next (native)
at onFulfilled (/home/vamsi/Do/koa-tutorial/node_modules/co/index.js:65:19)
at /home/vamsi/Do/koa-tutorial/node_modules/co/index.js:54:5
at new Promise (/home/vamsi/.nvm/v6.2.0/lib/node_modules/babel-cli/node_modules/core-js/modules/es6.promise.js:191:7)
at Object.co (/home/vamsi/Do/koa-tutorial/node_modules/co/index.js:50:10)
at converted (/home/vamsi/Do/koa-tutorial/node_modules/koa-convert/index.js:17:15)
at dispatch (/home/vamsi/Do/koa-tutorial/node_modules/koa/node_modules/koa-compose/index.js:43:32)
at next (/home/vamsi/Do/koa-tutorial/node_modules/koa/node_modules/koa-compose/index.js:44:18)
at _callee7$ (index.js:72:11)


The full code is on github. You can replace
body()
with
body2
in the code there.

UPDATE:



After doing a bit of additional logging, it says:

TypeError: next is not a function
at Object._callee3$ (index.js:29:11)
at tryCatch (/home/vamsi/.nvm/v6.2.0/lib/node_modules/babel-cli/node_modules/regenerator-runtime/runtime.js:62:40)
at GeneratorFunctionPrototype.invoke [as _invoke] (/home/vamsi/.nvm/v6.2.0/lib/node_modules/babel-cli/node_modules/regenerator-runtime/runtime.js:336:22)
at GeneratorFunctionPrototype.prototype.(anonymous function) [as next] (/home/vamsi/.nvm/v6.2.0/lib/node_modules/babel-cli/node_modules/regenerator-runtime/runtime.js:95:21)
at step (index.js:3:1)
at index.js:3:1
at new Promise (/home/vamsi/.nvm/v6.2.0/lib/node_modules/babel-cli/node_modules/core-js/modules/es6.promise.js:191:7)
at Object.<anonymous> (index.js:3:1)
at Object.backwards (index.js:25:7)
at Object.<anonymous> (/home/vamsi/Do/koa-tutorial/node_modules/koa-compose/index.js:25:28),

Answer

You are using a generator-based koa-compose for Koa 2, that won't work. You need koa-compose@3.x install it with:

npm install -S koa-compose@next