typescript/unbound-method Correctness

✅ This rule is turned on by default.

🚧 An auto-fix is still under development.

What it does

This rule enforces unbound methods are called with their expected scope.

Why is this bad?

When you extract a method from an object and call it separately, the this context is lost. This can lead to runtime errors or unexpected behavior, especially with methods that rely on this to access instance properties or other methods.

Examples

Examples of incorrect code for this rule:

class MyClass {
  private value = 42;

  getValue() {
    return this.value;
  }

  processValue() {
    return this.value * 2;
  }
}

const instance = new MyClass();

// Unbound method - loses 'this' context
const getValue = instance.getValue;
getValue(); // Runtime error: cannot read property 'value' of undefined

// Passing unbound method as callback
[1, 2, 3].map(instance.processValue); // 'this' will be undefined

// Destructuring methods
const { getValue: unboundGetValue } = instance;
unboundGetValue(); // Runtime error

Examples of correct code for this rule:

class MyClass {
  private value = 42;

  getValue() {
    return this.value;
  }

  processValue() {
    return this.value * 2;
  }
}

const instance = new MyClass();

// Call method on instance
const value = instance.getValue(); // Correct

// Bind method to preserve context
const boundGetValue = instance.getValue.bind(instance);
boundGetValue(); // Correct

// Use arrow function to preserve context
[1, 2, 3].map(() => instance.processValue()); // Correct

// Use arrow function in class for auto-binding
class MyClassWithArrow {
  private value = 42;

  getValue = () => {
    return this.value;
  };
}

const instance2 = new MyClassWithArrow();
const getValue = instance2.getValue; // Safe - arrow function preserves 'this'
getValue(); // Correct

How to use

To enable this rule in the CLI or using the config file, you can use:

CLI

oxlint --deny typescript/unbound-method

Config (.oxlintrc.json)

{
  "rules": {
    "typescript/unbound-method": "error"
  }
}

References

• Rule Source