Assert.that()

added in 0.0.1 • updated in 0.4.0 • last revisions

Syntax

function that(condition: boolean, failureMessage?: string): void

Asserts that an arbitrary condition is true by throwing an assertion error if it isn’t.

Parameters
`condition`	A condition that must evaluate to a boolean. If this condition is `false`, an assertion error is thrown.
`failureMessage` Optional	A failure message that will be thrown if the assertion fails. If not supplied, the failure message will be “`Assertion failed.`”

Example

import { Assert } from 'potence';

function removeSpaces(arg) {
    Assert.that(typeof arg === 'string', 'argument must be a string!');

    return arg.replace(' ', '');  // no error, arg is of type string
}

removeSpaces('fo  o');  // OK, returns 'foo'
removeSpaces(5);        // AssertionError: "Assertion failed: argument must be a string!"

Remarks

This function is a TypeScript assertion function meaning it behaves exactly the same as a condition in an if statement, narrowing the type if possible. This makes this function an extremely powerful tool to write one-liner assertion functions without having to use any type casts when using the variable afterwards.

You should still prefer one of the other assertion functions if possible, as the other functions typically have superior assertion error messages. For instance, prefer Assert.notNull() over Assert.that(x != null).