feat: add useCSSModule api (#420)

Author: yoyo930021

src/apis/index.ts

@@ -3,6 +3,7 @@ export * from './lifecycle'
 export * from './watch'
 export * from './computed'
 export * from './inject'
+export { useCSSModule } from './useCssModule'
 export { createApp } from './createApp'
 export { nextTick } from './nextTick'
 export { createElement as h } from './createElement'

src/apis/useCssModule.ts

@@ -0,0 +1,23 @@
+import { getCurrentInstance } from '../runtimeContext'
+import { warn } from '../utils'
+
+const EMPTY_OBJ: { readonly [key: string]: string } = __DEV__
+  ? Object.freeze({})
+  : {}
+
+export const useCSSModule = (name = '$style'): Record<string, string> => {
+  const instance = getCurrentInstance()
+  if (!instance) {
+    __DEV__ && warn(`useCSSModule must be called inside setup()`)
+    return EMPTY_OBJ
+  }
+
+  const mod = (instance as any)[name]
+  if (!mod) {
+    __DEV__ &&
+      warn(`Current instance does not have CSS module named "${name}".`)
+    return EMPTY_OBJ
+  }
+
+  return mod as Record<string, string>
+}