functionAssignments

Reports reassigning variables declared with function declarations.

✅ This rule is included in the ts untyped preset.

Reassigning a function declaration can make code harder to understand and maintain. Function declarations are hoisted to the top of their scope, and reassigning them can lead to unexpected behavior.

Examples

❌ Incorrect

function calculate(value: number): number {
  return value * 2;
}

calculate = (value: number) => value * 3;

function processData(): void {
  console.log("Processing...");
}

processData = null;

function getValue(): number {
  return 42;
}

getValue++;

✅ Correct

function calculate(value: number): number {
  return value * 2;
}

const result = calculate(10);

const processData = function (): void {
  console.log("Processing...");
};

processData = () => {
  console.log("Different processing");
};

let getValue = (): number => {
  return 42;
};

getValue = () => 100;

Options

This rule is not configurable.

When Not To Use It

If you’re working in an existing codebase where reassigning function declarations is a common pattern and refactoring would be too costly, you might choose to disable this rule. However, using function expressions or const variables is generally a better practice when reassignment is needed.

Further Reading

• MDN: Function declarations
• MDN: Function hoisting

Equivalents in Other Linters

• Biome: noFunctionAssign
• Deno: no-func-assign
• ESLint: no-func-assign
• Oxlint: eslint/no-func-assign