`@brillout/libassert`

Tiny zero-dependency tool for library authors to create assertion functions with clean strack traces.

Complete stack traces. (Error.stackTraceLimit = Infinity; only for assertion errors.)
Cleaned stack traces. (Fist stack line points to the assertion breaking code, useless stack lines are stripped away.)
Error messages are guaranteed to not contain new lines.

import { newError } from "@brillout/libassert";

export { assert };

function assert(condition: unknown): asserts condition {
  if (condition) {
    return;
  }

  const err = newError(
    `[${libName}][Internal Error] Something unexpected happened, please open a GitHub issue.`;
  );

  throw err;
}

Calling newError(errorMessage) is the same than new Error(errorMessage) except that:

The stack trace is complete and cleaned as described above.
errorMessage is forbidden to contain new lines.

You can create all kinds of assertion functions, such as assertUsage or assertWarning:

import { newError } from "@brillout/libassert";

export { assert, assertUsage, assertWarning };

const libName = "My Awesome Library";

// Assertions that are expected to always be true (also known as "invariants")
function assert(condition: unknown): asserts condition {
  if (condition) {
    return;
  }

  const err = newError(
    `[${libName}][Internal Error] Something unexpected happened, please open a GitHub issue.`;
  );

  throw err;
}

// Wrong usage of your library
function assertUsage(
  condition: unknown,
  errorMessage: string
): asserts condition {
  if (condition) {
    return;
  }

  const err = newError(prefix: `[${libName}][Wrong Usage] ${errorMessage}`);

  throw err;
}

// Something unexpected happened but it is non-critical and doesn't
// warrant interrupting code execution.
function assertWarning(condition: unknown, errorMessage: string): void {
  if (condition) {
    return;
  }

  const err = newError(`[${libName}][Warning] ${errorMessage}`);

  console.warn(err);
}