globalAssignments

Reports attempting to assign to read-only global variables such as undefined, NaN, Infinity, Object, etc.

✅ This rule is included in the ts untyped preset.

Global variables like undefined, NaN, Infinity, and built-in objects like Object and Array are read-only and should not be modified. Attempting to reassign these globals can lead to confusing behavior and potential bugs in your code. In strict mode, reassigning these globals will throw a TypeError at runtime.

Examples

❌ Incorrect

undefined = 1;

NaN = 42;

Infinity = 100;

Object = null;

Array = function () {};

let count = 5;
undefined += count;

NaN++;

--Infinity;

✅ Correct

let myUndefined = 1;

const notANumber = 42;

const infiniteValue = 100;

let myObject = null;

const myArray = function () {};

let count = 5;
let undefinedValue = undefined;
undefinedValue = count;

let notANumber = NaN;
notANumber++;

let infiniteValue = Infinity;
--infiniteValue;

Options

This rule is not configurable.

When Not To Use It

This rule should always be enabled, as attempting to reassign read-only global variables is always incorrect behavior in JavaScript and TypeScript. Modern JavaScript environments enforce these restrictions in strict mode, and violating them can cause runtime errors.

Further Reading

• MDN documentation on global objects
• MDN JavaScript Reference: Strict mode

Equivalents in Other Linters

• Biome: noGlobalAssign
• Deno: no-global-assign
• ESLint: no-global-assign
• Oxlint: eslint/no-global-assign