Use Boolean() for explicit boolean coercion · fabricahq/public-rules

When to apply Before writing, changing, or reviewing TypeScript code that converts a value to a boolean, such as !!value, or tests a value's truthiness.

When code intentionally converts a value to a boolean from its truthiness, write Boolean(value) instead of !!value. When the condition has a specific meaning, such as "present" or "non-empty", write that comparison instead of coercing.

Implementation

Replace !!value with Boolean(value).
Compare against the specific absent value, such as value !== undefined, when you need TypeScript to narrow the variable afterward; Boolean(value) in a separate variable does not narrow it.
Keep domain comparisons, such as count > 0, name.trim() !== '', or status === 'ready'; they say which condition matters.

This is a readability convention.

Rationale

Boolean(value) names the intent and is easy to search for, while !! is a symbol pair that readers can overlook. Truthiness also treats 0, '', and NaN as false, which is often not what a condition means; an explicit comparison makes the excluded cases visible.

Examples

Incorrect (counterexample):

const hasAccount = !!accountContext;

Correct:

const hasAccount = Boolean(accountContext);
const canView = accountContext !== undefined && sharedFile.allowedAccountIds.includes(accountContext.id);

Validation

Search for !! and replace intentional coercions with Boolean() or a specific comparison.

A specific comparison, such as count > 0, is not a violation.