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Severity: error
Category: null-safety
Stage: Stage 1

Description

The TypeScript non-null assertion operator (expr!) is not valid SJS syntax. It silently strips null | undefined from a type at the call site without any runtime check, defeating null safety.

Narrow explicitly with a conditional or early return.

Example

// ✗ error
const el = document.getElementById("app")!    // SJS-E011
el.innerHTML = "hello"

Fix

// ✓ correct — narrow explicitly
const el = document.getElementById("app")
if (el === null) throw new Error("Required element #app not found")
el.innerHTML = "hello"

// or with early return
function init(): void {
  const el = document.getElementById("app")
  if (el === null) return
  el.innerHTML = "hello"
}

Related codes

  • SJS-E001 — null assigned to non-nullable type
  • SJS-E003 — property access on possibly-null value
Documentation