Added onInit and useInitialized hooks

packages/svelte/src/lib/container/SvelteFlow/SvelteFlow.svelte

@@ -77,6 +77,7 @@
   export let onconnectstart: $$Props['onconnectstart'] = undefined;
   export let onconnectend: $$Props['onconnectend'] = undefined;
   export let onbeforedelete: $$Props['onbeforedelete'] = undefined;
+  export let oninit: $$Props['oninit'] = undefined;
 
   export let defaultMarkerColor = '#b1b1b7';
 
@@ -130,6 +131,16 @@
     }
   }
 
+  // Call oninit once when flow is intialized
+  const { initialized } = store;
+  let onInitCalled = false;
+  $: {
+    if (!onInitCalled && $initialized) {
+      oninit?.();
+      onInitCalled = true;
+    }
+  }
+
   // this updates the store for simple changes
   // where the prop names equals the store name
   $: {

packages/svelte/src/lib/container/SvelteFlow/types.ts

@@ -333,4 +333,6 @@ export type SvelteFlowProps = DOMAttributes<HTMLDivElement> & {
   onconnectstart?: OnConnectStart;
   /** When a user stops dragging a connection line, this event gets fired. */
   onconnectend?: OnConnectEnd;
+  /** This handler gets called when the flow is finished initializing */
+  oninit?: () => void;
 };