API Reference > bentleyjs-core > Utils > assert assert Function Asserts that a condition is true, and in development builds throws an error if it is not. This is an assertion function that alters the behavior of the TypeScript compiler. assert(condition: boolean, msg?: string): condition throws Error containing the specified message if condition is false. note This function should be used to validate conditions that should never realistically occur, or which indicate a misuse of the API which should be eliminated during development. Parameter Type Description condition boolean The result of a boolean expression. msg string An optional message to include in the thrown exception. Defaults to "Programmer Error". Returns - condition Defined in core/bentley/src/Assert.ts Line 20 Last Updated: 29 November, 2022