TypeScript Assertion Patterns

Type assertions tell TS: trust me, I know the type. ## Basic assertion ```ts const el = document.getElementById("app") as HTMLDivElement; el.innerHTML = "Hello"; ``` ## Angle bracket (not in JSX) ```ts const val = <string>someValue; ``` ## Dangerous example ```ts const n = "hello" as unknown as number; ``` This can break logic. ## Safer pattern: runtime check ```ts const el = document.getElementById("app"); if (el instanceof HTMLDivElement) { el.innerHTML = "Safe"; } ``` ## Graph ```mermaid flowchart TD A[Unknown Value] --> B[Assertion] B --> C[Trusted Type] ``` ## Remember - Assertions bypass checks - Prefer type guards first - Use only when you are sure