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Stopping execution

Throw errors to stop execution with recoverable errors

API

Stopping execution with panic errors​

warning

Use with caution. See explanation

panic(error) is equivalent to throw error statement.

But as a function, it has the advantages :

  • it can be used as an expression (ex: in ternary operator)
  • it can be used as a parameter (ex: as a callback)
  • it has a better semantic, implying that the program should stop
import { panic } from '@w5s/error';

function unsafeAsNotNullable(value: unknown) {
  return value ?? panic(new TypeError('Value must not be nullable'));
}

Stopping execution with a condition (assertion)​

warning

Use with caution. See explanation

invariant can be used to assert a condition. If the condition is false, it will throw an error with a descriptive message.

invariant(
  condition, 
  // ✓ Describe what is wrong
  // ✓ Add a hint on how to fix it
  // ✓ Starts with upper case character
  // ex: '"A" is not a valid integer', 'Unexpected parameter "foo_bar"', ...
  '{{Invariant message}}'
);

Example

import { invariant } from '@w5s/error';

function program() {
  invariant(true, 'This will not throw an error'); 
  // -> nothing
  invariant(false, 'This will throw an error'); 
  // -> throw InvariantError { message: 'Input should not be null' } when input is null or undefined

  //... do something with input
}

FAQ​

warning

Use throw with caution : when the program should be stopped​

In general, throwing errors is discouraged, instead Result should be used.

Nevertheless, errors can be thrown when :

  • Some condition is detected during runtime and the program cannot continue (i.e. assertion)
  • Program is in an impossible logical state and should be stopped (i.e. panic)