Connection Validation ​
To validate connections before they are created you can either pass a function to the is-valid-connection prop of the <Handle /> component or use the onConnect event of the <VueFlow /> component.
Another alternative is to pass a isValidConnection function to the is-valid-connection prop of the <VueFlow /> component. This function will be applied to all connections in the flow (even existing ones).
Using a handle in a custom node ​
vue
<div>
<!-- ... -->
<Handle type="source" :is-valid-connection="isValidConnection"/>
</div>