@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);
}