docs：更新文档

node_modules/koa-convert/index.js

@@ -0,0 +1,60 @@
+'use strict'
+
+const co = require('co')
+const compose = require('koa-compose')
+
+module.exports = convert
+
+function convert (mw) {
+  if (typeof mw !== 'function') {
+    throw new TypeError('middleware must be a function')
+  }
+  if (mw.constructor.name !== 'GeneratorFunction') {
+    // assume it's Promise-based middleware
+    return mw
+  }
+  const converted = function (ctx, next) {
+    return co.call(ctx, mw.call(ctx, createGenerator(next)))
+  }
+  converted._name = mw._name || mw.name
+  return converted
+}
+
+function * createGenerator (next) {
+  return yield next()
+}
+
+// convert.compose(mw, mw, mw)
+// convert.compose([mw, mw, mw])
+convert.compose = function (arr) {
+  if (!Array.isArray(arr)) {
+    arr = Array.from(arguments)
+  }
+  return compose(arr.map(convert))
+}
+
+convert.back = function (mw) {
+  if (typeof mw !== 'function') {
+    throw new TypeError('middleware must be a function')
+  }
+  if (mw.constructor.name === 'GeneratorFunction') {
+    // assume it's generator middleware
+    return mw
+  }
+  const converted = function * (next) {
+    let ctx = this
+    let called = false
+    // no need try...catch here, it's ok even `mw()` throw exception
+    yield Promise.resolve(mw(ctx, function () {
+      if (called) {
+        // guard against multiple next() calls
+        // https://github.com/koajs/compose/blob/4e3e96baf58b817d71bd44a8c0d78bb42623aa95/index.js#L36
+        return Promise.reject(new Error('next() called multiple times'))
+      }
+      called = true
+      return co.call(ctx, next)
+    }))
+  }
+  converted._name = mw._name || mw.name
+  return converted
+}