prefer-hoisting-branch-code.md

prefer-hoisting-branch-code

📝 Prefer moving code shared by all branches of an if statement out of the branches.

💼🚫 This rule is enabled in the ✅ recommended config. This rule is disabled in the ☑️ unopinionated config.

🔧💡 This rule is automatically fixable by the --fix CLI option and manually fixable by editor suggestions.

When every branch of an if/else if/else chain begins or ends with the same code, that code does not depend on the condition and only adds duplication. Moving it out of the branches keeps each branch focused on what is actually different.

This rule compares branch statements by token and AST structure, so it ignores comments, formatting, and optional trailing semicolons unless they change how the code is parsed. It only reports a complete chain (one with a final else), and only when every branch keeps at least one distinct statement, so it never empties a branch. Fully identical branches are left to unicorn/no-duplicate-if-branches.

Shared trailing code is auto-fixed, since it already runs after each branch's own code. Shared leading code is only offered as a suggestion when it has side effects, because moving it before the if runs it before the conditions are evaluated, which can change behavior:

// Moving the shared `counter += 1` before the `if` would change which branch runs.
if (counter === 0) {
	counter += 1;
	first();
} else {
	counter += 1;
	second();
}

The fix is skipped when it would change scope (the shared code declares a let/const/class, or trailing code references a variable declared earlier in the branch) or drop a comment.

Examples

// ❌
if (isAdmin) {
	log('access');
	showDashboard();
} else {
	log('access');
	showLogin();
}

// ✅
log('access');
if (isAdmin) {
	showDashboard();
} else {
	showLogin();
}

// ❌
if (isAdmin) {
	showDashboard();
	cleanup();
} else {
	showLogin();
	cleanup();
}

// ✅
if (isAdmin) {
	showDashboard();
} else {
	showLogin();
}

cleanup();

Related rules

• unicorn/no-duplicate-if-branches reports whole branches that are identical. This rule reports code shared only at the start or end of branches that otherwise differ.