API Reference › core-bentley › Utils › assert

assert Function

Asserts that a condition is true and - when enabled - throws an error if it is not.

Assertions are enabled only if the build configuration defines process.env.NODE_ENV as development at build time.

Assertions exist solely to assist programmers during development, in the following ways: 1 They allow the programmer to declare conditions that they believe cannot possibly occur. If such conditions occur, they indicate a serious flaw in the programmer's logic. 2 They allow the programmer to assure the TypeScript compiler of the truth of some condition that the compiler cannot itself infer. 3 They allow the author of an API to indicate to consumers of the API a serious misuse that should be corrected during development.

Assertions should never be used to test for conditions - however unlikely - that could be expected to occur at run-time, such as failing to write to a file or load a resource over the network. If the condition asserted ever fails in a production environment, the programmer has made a serious mistake.

Note that even when assertions are disabled, calls to assert remain in the code and their arguments will be evaluated at run-time. Therefore, if your condition or message requires computation, prefer to pass it as a function to prevent it from being evaluated when assertions are disabled.

assert(condition: boolean | () => boolean, message?: string | () => string): condition

@throws Error containing the specified message if condition is false.

Parameter Type Description
condition boolean | () => boolean The condition that is asserted to be true. If the condition is more complex than a simple boolean variable, pass it as a function to prevent it from being evaluated when assertions are disabled.
message string | () => string An optional description of the condition being asserted, to be included in the exception if condition is false. If the message must be computed, pass it as a function to prevent it from being evaluated when assertions are disabled. Defaults to "Programmer Error".

Returns - condition

Defined in

Last Updated: 25 April, 2024