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Misleading indentation of dangling ‘else’

ID: js/misleading-indentation-of-dangling-else
Kind: problem
Security severity: 
Severity: warning
Precision: very-high
Tags:
   - readability
   - statistical
   - non-attributable
   - external/cwe/cwe-483
Query suites:
   - javascript-security-and-quality.qls

Click to see the query in the CodeQL repository

In JavaScript, an else clause is always associated with the closest preceding if statement that does not already have an else clause. It is good practice to use indentation to clarify this structure by indenting matching if … else pairs by the same amount of whitespace.

Indenting the else clause of a nested if statement to suggest that it matches an outer if statement (instead of the one it actually belongs to) is confusing to readers and may even indicate a bug in the program logic.

Recommendation

Ensure that matching if … else pairs are indented accordingly.

Example

In the following example, the else on line 5 belongs to the if on line 3, while its indentation wrongly suggests that it belongs to the if on line 2.

function f() {
	if (cond1())
		if (cond2())
			return 23;
	else
		return 42;
	return 56;
}

To correct this issue, indent the else on line 5 further:

function f() {
	if (cond1())
		if (cond2())
			return 23;
		else
			return 42;
	return 56;
}

Confusion about which if belongs to which else can also be avoided by always enclosing the branches of an if statement in curly braces:

function f() {
	if (cond1()) {
		if (cond2()) {
			return 23;
		} else {
			return 42;
		}
	}
	return 56;
}

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