assert

Asserts that a given condition is true. If the condition is false, an error is thrown with the provided message or error.

This function is an alias for the invariant function.

Signature

function assert(condition: unknown, message: string): asserts condition;
function assert(condition: unknown, error: Error): asserts condition;

Parameters

• condition (unknown): The condition to evaluate.
• message (string | Error): The error message to throw if the condition is false.

Returns

(void): Returns void if the condition is true.

Throws

Throws an error with the specified message if the condition evaluates to false.

Examples

// This call will succeed without any errors
assert(true, 'This should not throw');

// This call will fail and throw an error with the message 'This should throw'
assert(false, 'This should throw');

// Example of using assert with a condition
assert(condition, 'Expected condition is false');

// Ensure that the value is neither null nor undefined
assert(value !== null && value !== undefined, 'Value should not be null or undefined');

// Example of using assert to check if a number is positive
assert(number > 0, 'Number must be positive');

// Example of using assert with an error
assert(false, new Error('This should throw'));

// Example of using assert with a custom error
class CustomError extends Error {
  constructor(message: string) {
    super(message);
  }
}

assert(false, new CustomError('This should throw'));