Added on used support

index.js

@@ -30,7 +30,7 @@ function compose (middleware) {
    * @api public
    */
 
-  return function (context, next) {
+  let ret = function (context, next) {
     // last called middleware #
     let index = -1
     return dispatch(0)
@@ -48,4 +48,10 @@ function compose (middleware) {
       }
     }
   }
+  ret.onUsed = function (useCtx) {
+    if (useCtx.prepareMiddleware) {
+      middleware = middleware.map((mw) => useCtx.prepareMiddleware(mw))
+    }
+  }
+  return ret
 }

test/test.js

@@ -256,4 +256,24 @@ describe('Koa Compose', function () {
       val.should.equal(1)
     })
   })
+
+  it('should accept any onUsed object', function () {
+    var composed = compose([(ctx, next) => next()])
+    composed.onUsed({})
+    return composed({})
+  })
+
+  it('should prepare the middleware', function () {
+    var mw = (ctx) => { ctx.body = 'body' }
+    var composed = compose([mw])
+    var useContext = {
+      app: {},
+      useChain: [],
+      prepareMiddleware: function (toPrepare) {
+        assert.equal(toPrepare, mw)
+      }
+    }
+    composed.onUsed(useContext)
+    return composed({}, () => {})
+  })
 })