nonfalsy

Nonfalsy is a term used in programming to describe values that evaluate to true in a boolean context. It denotes the opposite of falsy values. Because truthiness rules differ by language, what counts as nonfalsy is not universal. In practice, nonfalsy values are those that allow a conditional, a loop, or a logical expression to proceed.

JavaScript defines a separate list of falsy values: false, 0, -0, 0n, '', null, undefined, and NaN. Every other value is nonfalsy. This includes true, nonzero numbers, non-empty strings, objects, arrays, and functions. Note that in JavaScript, empty arrays and empty objects are truthy, and string values such as '0' are truthy.

In Python, falsy values include False, None, 0, 0.0, empty strings, lists, tuples, dictionaries, sets, and any object whose __bool__ method returns False or whose __len__ returns zero. All other values are nonfalsy, such as nonzero numbers, non-empty strings, and non-empty containers. Unlike JavaScript, float('nan') is truthy in Python, so NaN evaluates to True in a boolean context.

Nonfalsy values are commonly used in conditionals and filtering. Relying on truthiness can simplify code but may reduce readability or cause bugs if the meaning of empty or zero is significant. When a specific value matters, explicit checks (for example, value is not None, or len(value) > 0) can improve clarity.