Assert in Dart

Assert

While coding, it is hard to find errors in big projects, so dart provide a assert method to check for the error. It takes conditions as an argument. If the condition is true, nothing happens. If a condition is false, it will raise an error.

Syntax

You can use assert without a custom message or with a custom message.

assert(condition);
// or 
assert(condition, "Your custom message");

Example 1: How To Use Assert In Dart Program

This example shows how you can use assert without a custom message.

void main() { 
   var age = 22;
   assert(age!=22);
}

Uncaught Error: Assertion failed

Example 2: How To Use Assert In Dart Program

This example shows how you can use assert with a custom message.

void main() { 
   var age = 22;
   assert(age!=22, "Age must be 22");
}

Uncaught Error: Assertion failed: "Age must be 22"

How to Run File In Assert Mode

Use this command to run the dart file, which enables assert. If you don’t use this, you will not be able to see the issue. You can use this command below if you are running a dart file from the computer.

dart --enable-asserts file_name.dart

Video

Watch our video on the assert in Dart.