[feat] add convenience types ComponentType and ComponentProps

CHANGELOG.md

@@ -5,6 +5,7 @@
 * Faster SSR ([#5701](https://github.com/sveltejs/svelte/pull/5701))
 * Fix `class:` directive updates with `<svelte:element>` ([#7521](https://github.com/sveltejs/svelte/issues/7521), [#7571](https://github.com/sveltejs/svelte/issues/7571))
 * Harden attribute escaping during ssr ([#7530](https://github.com/sveltejs/svelte/pull/7530))
+* Add `ComponentType` convenience type ([#6770](https://github.com/sveltejs/svelte/pull/6770))
 
 ## 3.48.0
 

package.json

@@ -95,7 +95,7 @@
     "pretest": "npm run build",
     "posttest": "agadoo internal/index.mjs",
     "prepublishOnly": "node check_publish_env.js && npm run lint && npm test",
-    "tsd": "tsc -p src/compiler --emitDeclarationOnly && tsc -p src/runtime --emitDeclarationOnly",
+    "tsd": "node ./tsd.js",
     "lint": "eslint \"{src,test}/**/*.{ts,js}\""
   },
   "repository": {

src/runtime/index.ts

@@ -13,4 +13,5 @@ export {
 	createEventDispatcher,
 	SvelteComponentDev as SvelteComponent,
 	SvelteComponentTyped
+	// additional exports added through post-typegen.js
 } from 'svelte/internal';

src/runtime/internal/dev.ts

@@ -128,7 +128,7 @@ export interface SvelteComponentDev {
 	$destroy(): void;
 	[accessor: string]: any;
 }
-interface IComponentOptions<Props extends Record<string, any> = Record<string, any>> {
+export interface ComponentConstructorParams<Props extends Record<string, any> = Record<string, any>> {
 	target: Element | ShadowRoot;
 	anchor?: Element;
 	props?: Props;
@@ -164,7 +164,7 @@ export class SvelteComponentDev extends SvelteComponent {
 	 */
 	$$slot_def: any;
 
-	constructor(options: IComponentOptions) {
+	constructor(options: ComponentConstructorParams) {
 		if (!options || (!options.target && !options.$$inline)) {
 			throw new Error("'target' is a required option");
 		}
@@ -256,11 +256,47 @@ export class SvelteComponentTyped<
 	 */
 	$$slot_def: Slots;
 
-	constructor(options: IComponentOptions<Props>) {
+	constructor(options: ComponentConstructorParams<Props>) {
 		super(options);
 	}
 }
 
+/**
+ * Convenience type to get the type of a Svelte component. Useful for example in combination with
+ * dynamic components and `<svelte:element>`.
+ * 
+ * Example:
+ * ```html
+ * <script lang="ts">
+ * 	import type { ComponentType, SvelteComponentTyped } from 'svelte';
+ * 	import Component1 from './Component1.svelte';
+ * 	import Component2 from './Component2.svelte';
+ * 
+ * 	const component: ComponentType = someLogic() ? Component1 : Component2;
+ * 	const componentOfCertainSubType: ComponentType<SvelteComponentTyped<{ needsThisProp: string }>> = someLogic() ? Component1 : Component2;
+ * </script>
+ * 
+ * <svelte:element this={component} />
+ * <svelte:element this={componentOfCertainSubType} needsThisProp="hello" />
+ * ```
+ */
+export type ComponentType<T extends SvelteComponentTyped = SvelteComponentTyped<any, any, any>> =
+	new (p: ComponentConstructorParams<T extends SvelteComponentTyped<infer X, any, any> ? X : any>) => T;
+
+ * Convenience type to get the props the given component expects. Example:
+ * ```html
+ * <script lang="ts">
+ * 	import type { ComponentProps } from 'svelte';
+ * 	import Component from './Component.svelte';
+ * 
+ * 	const props: ComponentProps<Component> = { foo: 'bar' }; // Errors if these aren't the correct props
+ * </script>
+ * ```
+ */
+export type ComponentProps<T extends SvelteComponent> = T extends SvelteComponentTyped<infer Props>
+	? Props
+	: unknown;
+
 export function loop_guard(timeout) {
 	const start = Date.now();
 	return () => {

tsd.js

@@ -0,0 +1,13 @@
+// This script generates the TypeScript definitions
+
+const { execSync } = require('child_process');
+const { readFileSync, writeFileSync } = require('fs');
+
+execSync('tsc -p src/compiler --emitDeclarationOnly && tsc -p src/runtime --emitDeclarationOnly');
+
+// We need to add these types to the index.d.ts here because if we add them before building, the build will fail,
+// because the TS->JS transformation doesn't know these exports are types and produces code that fails at runtime.
+// We can't use `export type` syntax either because the TS version we're on doesn't have this feature yet.
+const path = 'types/runtime/index.d.ts';
+const content = readFileSync(path, 'utf8');
+writeFileSync(path, content.replace('SvelteComponentTyped', 'SvelteComponentTyped, ComponentType, ComponentConstructorParams, ComponentProps'));