Validation

<script lang="ts">
  import { writable } from 'svelte/store';
  import {
    SvelteFlow,
    Controls,
    Background,
    BackgroundVariant,
    type IsValidConnection,
    Position
  } from '@xyflow/svelte';
 
  import '@xyflow/svelte/dist/style.css';
 
  const nodeDefaults = {
    sourcePosition: Position.Right,
    targetPosition: Position.Left
  };
 
  const nodes = writable([
    {
      id: '0',
      position: { x: 0, y: 150 },
      data: { label: 'only connectable with B' },
      ...nodeDefaults
    },
    {
      id: 'A',
      position: { x: 250, y: 0 },
      data: { label: 'A' },
      ...nodeDefaults
    },
    {
      id: 'B',
      position: { x: 250, y: 150 },
      data: { label: 'B' },
      ...nodeDefaults
    },
    {
      id: 'C',
      position: { x: 250, y: 300 },
      data: { label: 'C' },
      ...nodeDefaults
    }
  ]);
 
  const edges = writable([]);
 
  const isValidConnection: IsValidConnection = (connection) => connection.target === 'B';
</script>
 
<main>
  <SvelteFlow {nodes} {edges} fitView minZoom={0.1} maxZoom={2.5} {isValidConnection}>
    <Controls />
    <Background variant={BackgroundVariant.Dots} />
  </SvelteFlow>
</main>
 
<style>
  main {
    height: 100vh;
  }
 
  :global(.svelte-flow .svelte-flow__node .svelte-flow__handle) {
    width: 8px;
    height: 8px;
  }
 
  :global(.svelte-flow .svelte-flow__handle.connectingto) {
    background: #ff6060;
  }
 
  :global(.svelte-flow .svelte-flow__handle.valid) {
    background: #55dd99;
  }
</style>