noUncheckedIndexedAccess enabled

noUncheckedIndexedAccess is not covered by the strict umbrella — it must be set explicitly, and most TypeScript projects never do. Without it, array[0] is typed as T even when the array is empty, so array[0].name compiles fine and throws Cannot read properties of undefined at runtime. ISO 25010:2011 §6.5.4 flags this as a reliability defect. This is one of the highest-signal, lowest-friction compiler flags available: it adds | undefined to every index access and forces you to handle the empty case.

Add "noUncheckedIndexedAccess": true to your tsconfig.json compilerOptions. It is not implied by strict: true, so it must be explicit. The flag will surface every unguarded array access — fix them with optional chaining or an explicit undefined check.

// Before (unsafe — crashes if items is empty):
const first = items[0].name;

// After (safe):
const first = items[0]?.name;
// or:
const item = items[0];
if (item !== undefined) { console.log(item.name); }

{
  "compilerOptions": {
    "strict": true,
    "noUncheckedIndexedAccess": true
  }
}

• ID: unchecked-indexed-access

• Severity: critical

• What to look for: In tsconfig.json compilerOptions, look for "noUncheckedIndexedAccess": true. This flag is not covered by the strict umbrella — it must be set explicitly. Without it, TypeScript treats array[0] as type T even when the array could be empty (it should be T | undefined). This is one of the most common sources of runtime undefined crashes in TypeScript codebases. Check that this option is set in the tsconfig.json that governs application source files (not just a test-specific config).

• Pass criteria: Enumerate all tsconfig files (root and workspace overrides). Quote the actual noUncheckedIndexedAccess value. noUncheckedIndexedAccess: true must be present in at least 100% of configs in the tsconfig covering application source files. On pass, report the count of tsconfig files verified.

• Fail criteria: The flag is absent or explicitly set to false. Having strict: true without explicitly adding noUncheckedIndexedAccess does not count as pass for this check.

• Skip (N/A) when: Project has no TypeScript files.

• Detail on fail: "noUncheckedIndexedAccess not set in tsconfig.json; array/object index access returns T instead of T | undefined"

• Remediation: Add the flag to tsconfig.json. It will surface places where you access array indices or record keys without checking for undefined first. Common patterns to fix:

  // Before (unsafe):
  const first = items[0].name; // crashes if items is empty
  
  // After (safe):
  const first = items[0]?.name;
  // or
  const item = items[0];
  if (item !== undefined) {
    console.log(item.name);
  }
  

  {
    "compilerOptions": {
      "strict": true,
      "noUncheckedIndexedAccess": true
    }
  }