constantAssignments

Reports attempting to reassign variables declared with const.

✅ This rule is included in the ts untyped preset.

The const keyword creates a read-only reference to a value, preventing reassignment. While properties of const objects and elements of const arrays can be mutated, the binding itself cannot be reassigned. Attempting to reassign a const variable results in a runtime error.

Examples

❌ Incorrect

const value = 1;
value = 2;

const result = getValue();
result = getOtherValue();

const counter = 0;
counter++;

const { property } = object;
property = "new value";

for (const item of items) {
  item = processItem(item);
}

✅ Correct

let value = 1;
value = 2;

const object = { value: 1 };
object.value = 2;

const array = [1, 2, 3];
array.push(4);

const { property } = object;
console.log(property);

for (let item of items) {
  item = processItem(item);
}

Options

This rule is not configurable.

When Not To Use It

This rule should always be enabled. Reassigning a const variable is a runtime error in JavaScript and TypeScript, so this rule helps catch such issues during development.

Further Reading

• MDN: const
• MDN: let

Equivalents in Other Linters

• Biome: noConstAssign
• Deno: no-const-assign
• ESLint: no-const-assign
• Oxlint: eslint/no-const-assign