Check if an Object is Truthy in Dart

If you are coming from language like JavaScript you may be used to checking if an object is truthy.

if (true) if ({}) if ([]) if (42) if ("0") if ("false") if (new Date()) if (-42) if (12n) if (3.14) if (-3.14) if (Infinity) if (-Infinity)

In Dart you need to explicitly check if an object is not null, true/false or determine if the value is true based on the type.

It is possible however to use Dart extensions to add the truthy capability.

extension on Object? { bool get isTruthy => truthy(this); }

bool truthy(Object? val) { if (val == null) return false; if (val is bool) return val; if (val is num && val == 0) return false; if (val is String && (val == 'false' || val == '')) return false; if (val is Iterable && val.isEmpty) return false; if (val is Map && val.isEmpty) return false; return true; }

This will now make it possible for any object to be evaluated as a truthy value in if statements or value assignments.

Prints the following:

(null, false) (, false) (false, false) (true, true) (0, false) (1, true) (false, false) (true, true) ([], false) ([1, 2, 3], true) ({}, false) ({1, 2, 3}, true) ({a: 1, b: 2}, true)

Demo