TypeScript Union Types

Union types let a variable hold **more than one type**. ## Why needed? In real apps, data is not always one shape. ## Example ```ts let id: number | string; id = 10; id = "A12"; ``` ## Using unions in functions ```ts function printId(id: number | string) { console.log(id); } ``` ## Narrowing ```ts function printId(id: number | string) { if (typeof id === "string") { console.log(id.toUpperCase()); } else { console.log(id.toFixed(2)); } } ``` ## With null ```ts let username: string | null = null; ``` ## Graph ```mermaid flowchart TD A[Union Type] --> B[string] A --> C[number] ``` ## Remember - Use unions for flexible APIs - Always narrow before using