feat(runtime-core): explicit expose API

packages/runtime-core/src/component.ts

@@ -105,7 +105,7 @@ export interface ComponentInternalOptions {
 export interface FunctionalComponent<P = {}, E extends EmitsOptions = {}>
   extends ComponentInternalOptions {
   // use of any here is intentional so it can be a valid JSX Element constructor
-  (props: P, ctx: SetupContext<E>): any
+  (props: P, ctx: Omit<SetupContext<E>, 'expose'>): any
   props?: ComponentPropsOptions<P>
   emits?: E | (keyof E)[]
   inheritAttrs?: boolean
@@ -171,6 +171,7 @@ export interface SetupContext<E = EmitsOptions> {
   attrs: Data
   slots: Slots
   emit: EmitFn<E>
+  expose: (exposed: Record<string, any>) => void
 }
 
 /**
@@ -270,6 +271,9 @@ export interface ComponentInternalInstance {
   // main proxy that serves as the public instance (`this`)
   proxy: ComponentPublicInstance | null
 
+  // exposed properties via expose()
+  exposed: Record<string, any> | null
+
   /**
    * alternative proxy used only for runtime-compiled render functions using
    * `with` block
@@ -415,6 +419,7 @@ export function createComponentInstance(
     update: null!, // will be set synchronously right after creation
     render: null,
     proxy: null,
+    exposed: null,
     withProxy: null,
     effects: null,
     provides: parent ? parent.provides : Object.create(appContext.provides),
@@ -731,6 +736,13 @@ const attrHandlers: ProxyHandler<Data> = {
 }
 
 function createSetupContext(instance: ComponentInternalInstance): SetupContext {
+  const expose: SetupContext['expose'] = exposed => {
+    if (__DEV__ && instance.exposed) {
+      warn(`expose() should be called only once per setup().`)
+    }
+    instance.exposed = proxyRefs(exposed)
+  }
+
   if (__DEV__) {
     // We use getters in dev in case libs like test-utils overwrite instance
     // properties (overwrites should not be done in prod)
@@ -743,13 +755,15 @@ function createSetupContext(instance: ComponentInternalInstance): SetupContext {
       },
       get emit() {
         return (event: string, ...args: any[]) => instance.emit(event, ...args)
-      }
+      },
+      expose
     })
   } else {
     return {
       attrs: instance.attrs,
       slots: instance.slots,
-      emit: instance.emit
+      emit: instance.emit,
+      expose
     }
   }
 }