Provide a helper to create custom decorators (#30)

* add create decorator helper

* update readme for createDecorator helper

Author: ktsn

Diff for: README.md

@@ -64,6 +64,40 @@ class App {
 
 You may also want to check out the `@prop` and `@watch` decorators provided by [vue-property-decorators](https://github.com/kaorun343/vue-property-decorator).
 
+### Create Custom Decorators
+
+You can extend the functionality of this library by creating your own decorators. vue-class-component provides `createDecorator` helper to create custom decorators. `createDecorator` expects a callback function as the 1st argument and the callback will receive following arguments:
+
+- `options`: Vue component options object. Changes for this object will affect the provided component.
+- `key`: The property or method key that the decorator is applied.
+- `parameterIndex`: The index of a decorated argument if the custom decorator is used for an argument.
+
+Example of creating `NoCache` decorator:
+
+``` js
+// decorators.js
+import { createDecorator } from 'vue-class-component'
+
+export const NoCache = createDecorator((options, key) => {
+  // component options should be passed to the callback
+  // and update for the options object affect the component
+  options.computed[key].cache = false
+})
+```
+
+``` js
+import { NoCache } from './decorators'
+
+@Component
+class MyComp extends Vue {
+  // the computed property will not be cached
+  @NoCache
+  get random () {
+    return Math.random()
+  }
+}
+```
+
 ### Build the Example
 
 ``` bash

Diff for: src/component.ts

@@ -17,6 +17,11 @@ const internalHooks = [
   'render'
 ]
 
+// Property, method and parameter decorators created by `createDecorator` helper
+// will enqueue functions that update component options for lazy processing.
+// They will be executed just before creating component constructor.
+export let $decoratorQueue: ((options: Vue.ComponentOptions<Vue>) => void)[] = []
+
 export function componentFactory (
   Component: VueClass,
   options: Vue.ComponentOptions<any> = {}
@@ -53,6 +58,11 @@ export function componentFactory (
     }
   })
 
+  // decorate options
+  $decoratorQueue.forEach(fn => fn(options))
+  // reset for other component decoration
+  $decoratorQueue = []
+
   // find super
   const superProto = Object.getPrototypeOf(Component.prototype)
   const Super: VueClass = superProto instanceof Vue

Diff for: src/data.ts

@@ -1,7 +1,6 @@
 import * as Vue from 'vue'
 import { VueClass } from './declarations'
-
-const noop = () => {}
+import { noop } from './util'
 
 export function collectDataFromConstructor (vm: Vue, Component: VueClass) {
   // Create dummy Vue instance to collect

Diff for: src/index.ts

@@ -3,6 +3,8 @@ import { VueClass } from './declarations'
 
 import { componentFactory } from './component'
 
+export { createDecorator } from './util'
+
 export default function Component <U extends Vue>(options: Vue.ComponentOptions<U>): <V extends VueClass>(target: V) => V
 export default function Component <V extends VueClass>(target: V): V
 export default function Component <V extends VueClass>(options: Vue.ComponentOptions<any> | V): any {

Diff for: src/util.ts

@@ -0,0 +1,21 @@
+import * as Vue from 'vue'
+import { $decoratorQueue } from './component'
+
+export const noop = () => {}
+
+export function createDecorator (
+  factory: (options: Vue.ComponentOptions<Vue>, key: string) => void
+): (target: Vue, key: string) => void
+export function createDecorator (
+  factory: (options: Vue.ComponentOptions<Vue>, key: string, index: number) => void
+): (target: Vue, key: string, index: number) => void
+export function createDecorator (
+  factory: (options: Vue.ComponentOptions<Vue>, key: string, index: number) => void
+): (target: Vue, key: string, index: any) => void {
+  return (_, key, index) => {
+    if (typeof index !== 'number') {
+      index = undefined
+    }
+    $decoratorQueue.push(options => factory(options, key, index))
+  }
+}

Diff for: test/test.ts

@@ -1,4 +1,4 @@
-import Component from '../lib/index'
+import Component, { createDecorator } from '../lib/index'
 import { expect } from 'chai'
 import * as Vue from 'vue'
 
@@ -143,4 +143,36 @@ describe('vue-class-component', () => {
     expect(a.a).to.equal(1)
     expect(a.b).to.equal(2)
   })
+
+  it('createDecorator', function () {
+    const Prop = createDecorator((options, key) => {
+      // component options should be passed to the callback
+      // and update for the options affect the component
+      (options.props || (options.props = {}))[key] = true
+    })
+
+    const NoCache = createDecorator((options, key) => {
+      // options should have computed and methods etc.
+      // that specified by class property accessors and methods
+      const computedOption: Vue.ComputedOptions<Vue> = options.computed![key]
+      computedOption.cache = false
+    })
+
+    @Component
+    class MyComp extends Vue {
+      @Prop foo: string
+      @NoCache get bar (): string {
+        return 'world'
+      }
+    }
+
+    const c = new MyComp({
+      propsData: {
+        foo: 'hello'
+      }
+    })
+    expect(c.foo).to.equal('hello')
+    expect(c.bar).to.equal('world')
+    expect((MyComp as any).options.computed.bar.cache).to.be.false
+  })
 })