prefer-default-parameters.md

Prefer default parameters over reassignment

✅ This rule is part of the recommended config.

🔧💡 This rule is auto-fixable and provides suggestions.

Instead of reassigning a function parameter, default parameters should be used. The foo = foo || 123 statement evaluates to 123 when foo is falsy, possibly leading to confusing behavior, whereas default parameters only apply when passed an undefined value. This rule only reports reassignments to literal values.

Fail

function abc(foo) {
	foo = foo || 'bar';
}

function abc(foo) {
	const bar = foo || 'bar';
}

Pass

function abc(foo = 'bar') {}

function abc(foo) {
	foo = foo || bar();
}