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Dart Boolean Tutorial with Examples

  1. Boolean
  2. Dart Boolean vs Javascript Boolean

1. Boolean

In the Dart programming language, bool is a supported data type, which only includes 2 values, true and false.
bool is also the name of the class representing this data type.
Syntax to declare a variable of bool type:
bool myVariable1 = true;

bool myVariable2 = false;
Example:
bool_ex1.dart
void main() {
  bool value;
  value = 100 > 25;
  print(value); // true
}
Output:
true

2. Dart Boolean vs Javascript Boolean

The Dart programming language borrows a lot of ideas from JavaScript, which is why it is so easily converted into JavaScript code. However, the bool data type in Dart and JavaScript has a few differences.
  • In JavaScript the values false, 0, "", null, undefined, NaN and Number.Infinite are considered false. Other values are considered true.
  • In Dart, only true and false are considered bool, other values cannot be converted to bool.
In JavaScript you can write code like below, which is accepted as valid:
Javascript code
var test = "abc";

if(test) {
   console.log("OK! test is true");
} else {
   console.log("Ohh no, test is false");
}
Output:
OK! test is true
However, you can't write a similar code in Dart:
Dart code (ERROR!)
void main() {
  var test = "abc";

  if (test) { // ERROR at compile time.
    print("OK! test is true");
  } else {
    print("Ohh no, test is false");
  }
}
You will get an error message from the Dart compiler:
Error compiling to JavaScript:
Warning: Interpreting this as package URI, 'package:dartpad_sample/main.dart'.
lib/main.dart:4:7:
Error: A value of type 'String' can't be assigned to a variable of type 'bool'.
  if (test) { // ERROR at compile time.
      ^
Error: Compilation failed.

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