90. Multi-Select Dropdown

Build a Multi-Select Dropdown in React that supports controlled multi-selection, query filtering, and deterministic open/close behavior.

1. Controlled Selection Contract

• Selection must be controlled by value + onChange.
• The component should never own a shadow selected-state source of truth.
• Toggling an option adds/removes its id immutably.

2. Dropdown Interaction Model

• Clicking trigger opens/closes the list.
• Clicking outside closes the list.
• Dropdown should stay open while selecting multiple options.

3. Search / Filter Projection

• Include an input for filtering options.
• Filtering must be case-insensitive and derived from source options.
• Selected options remain selected even when not visible under current query.

4. Clear and Summary UX

• Provide a summary in the trigger (placeholder or selected count).
• Provide a clear-all action that resets controlled selection.

5. Data Contract

interface Option {
  id: string;
  label: string;
}

interface MultiSelectProps {
  options: Option[];
  value: string[];
  onChange: (next: string[]) => void;
  placeholder?: string;
}

6. Example Seed

const sampleOptions: Option[] = [
  { id: "react", label: "React" },
  { id: "ts", label: "TypeScript" },
  { id: "node", label: "Node.js" },
  { id: "graphql", label: "GraphQL" }
];