AgentSkillsCN

check-if-an-object-is-truthy-in-dart

学习如何扩展 Dart 的功能，实现类似 JavaScript 的“真值”检查，从而简化条件逻辑与数值评估。

SKILL.md
--- frontmatter
name: check-if-an-object-is-truthy-in-dart
description: Learn how to extend Dart's functionality to implement JavaScript-style "truthy" checks for easier conditional logic and value evaluations.
metadata:
  url: https://rodydavis.com/posts/dart/truthy
  last_modified: Tue, 03 Feb 2026 20:04:34 GMT

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.

code
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.

code
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:

code
(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