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no-unnecessary-initialization

Disallow unnecessary initialization to undefined.

Targeted pattern scope​

This rule checks for explicit undefined initializers in two places:

  • let and var declarators with identifier bindings (let value = undefined;), and
  • class property definitions (field = undefined;).

Only direct identifier undefined is matched. const declarations and destructuring bindings are excluded because deleting their initializers would produce invalid syntax.

What this rule reports​

This rule reports eligible variables and class fields explicitly initialized with undefined.

Why this rule exists​

Initializing to undefined is usually redundant in JavaScript/TypeScript. Removing these initializers makes intent clearer and avoids unnecessary syntax.

❌ Incorrect​

let value = undefined;
class C {
 field = undefined;
}

✅ Correct​

let value: number | undefined;
class C {
 field?: number;
}

// Allowed because a const declaration requires an initializer.
const sentinel = undefined;

Behavior and migration notes​

This rule autofixes reports by deleting = undefined. It deliberately skips declarations for which that deletion would produce invalid JavaScript or TypeScript.

Options​

This rule has no options.

Additional examples​

let cache = undefined;
// ❌ reported

let cache: string | undefined;
// ✅ valid

ESLint flat config example​

import etcMisc from "eslint-plugin-etc-misc";

export default [
 {
  plugins: { "etc-misc": etcMisc },
  rules: {
   "etc-misc/no-unnecessary-initialization": "error",
  },
 },
];

When not to use it​

Disable this rule if your project prefers explicit undefined initializers for clarity.

Package documentation​

Rule catalog ID: R063

Further reading​

Adoption resources​

  • Start at warning level in CI, then move to error after cleanup.
  • Use focused codemods/autofix batches per package or directory.