assertcheck v0.6.0

---

assertcheck / AssertionError

Class: AssertionError

Defined in: src/error.ts:55

Error thrown when an assertion fails.

Remarks

Unlike a generic Error, AssertionError carries structured metadata about what was expected, what was received, and which assertion failed. This makes it easy to catch and inspect in tests or error boundaries.

The stack trace is cleaned up with Error.captureStackTrace (V8 / Node.js / Bun) so the first frame points directly to the call site that triggered the assertion — not to the internal fail() helper inside this library.

Example

import { assert, AssertionError } from "assertcheck"

try {
  assert.equal(order.status, "pending", "must be pending before payment")
} catch (err) {
  if (err instanceof AssertionError) {
    console.error("Assertion:", err.assertion) // "equal"
    console.error("Actual:",    err.actual)    // "paid"
    console.error("Expected:",  err.expected)  // "pending"
  }
}

Extends

• Error

Constructors

Constructor

new AssertionError(opts): AssertionError;

Defined in: src/error.ts:73

Parameters

Parameter	Type
opts	AssertionErrorOptions

Returns

AssertionError

Overrides

Error.constructor

Properties

Property	Modifier	Type	Description	Inherited from	Defined in
actual	readonly	unknown	The value that was actually received at the time of the assertion.	-	src/error.ts:65
assertion	readonly	string	Name of the assertion function that failed. Example "equal"`, `"all"`, `"hasExactKeys"	-	src/error.ts:60
cause?	public	unknown	The cause of the error.	Error.cause	node_modules/typescript/lib/lib.es2022.error.d.ts:26
expected	readonly	unknown	The value or constraint that was expected. May be a concrete value, a descriptive string, or undefined.	-	src/error.ts:71
message	public	string	-	Error.message	node_modules/typescript/lib/lib.es5.d.ts:1077
name	public	string	-	Error.name	node_modules/typescript/lib/lib.es5.d.ts:1076
stack?	public	string	-	Error.stack	node_modules/typescript/lib/lib.es5.d.ts:1078
stackTraceLimit	static	number	The Error.stackTraceLimit property specifies the number of stack frames collected by a stack trace (whether generated by new Error().stack or Error.captureStackTrace(obj)). The default value is 10 but may be set to any valid JavaScript number. Changes will affect any stack trace captured after the value has been changed. If set to a non-number value, or set to a negative number, stack traces will not capture any frames.	Error.stackTraceLimit	node_modules/@types/node/globals.d.ts:67

Methods

captureStackTrace()

Call Signature

static captureStackTrace(targetObject, constructorOpt?): void;

Defined in: node_modules/@types/node/globals.d.ts:51

Creates a .stack property on targetObject, which when accessed returns a string representing the location in the code at which Error.captureStackTrace() was called.

const myObject = {};
Error.captureStackTrace(myObject);
myObject.stack;  // Similar to `new Error().stack`

The first line of the trace will be prefixed with ${myObject.name}: ${myObject.message}.

The optional constructorOpt argument accepts a function. If given, all frames above constructorOpt, including constructorOpt, will be omitted from the generated stack trace.

The constructorOpt argument is useful for hiding implementation details of error generation from the user. For instance:

function a() {
  b();
}

function b() {
  c();
}

function c() {
  // Create an error without stack trace to avoid calculating the stack trace twice.
  const { stackTraceLimit } = Error;
  Error.stackTraceLimit = 0;
  const error = new Error();
  Error.stackTraceLimit = stackTraceLimit;

  // Capture the stack trace above function b
  Error.captureStackTrace(error, b); // Neither function c, nor b is included in the stack trace
  throw error;
}

a();

Parameters

Parameter	Type
targetObject	object
constructorOpt?	Function

Returns

void

Inherited from

Error.captureStackTrace

Call Signature

static captureStackTrace(targetObject, constructorOpt?): void;

Defined in: node_modules/bun-types/globals.d.ts:1042

Create .stack property on a target object

Parameters

Parameter	Type
targetObject	object
constructorOpt?	Function

Returns

void

Inherited from

Error.captureStackTrace

---

isError()

static isError(value): value is Error;

Defined in: node_modules/bun-types/globals.d.ts:1037

Check if a value is an instance of Error

Parameters

Parameter	Type	Description
value	unknown	The value to check

Returns

value is Error

True if the value is an instance of Error, false otherwise

Inherited from

Error.isError

---

prepareStackTrace()

static prepareStackTrace(err, stackTraces): any;

Defined in: node_modules/@types/node/globals.d.ts:55

Parameters

Parameter	Type
err	Error
stackTraces	CallSite[]

Returns

any

See

https://v8.dev/docs/stack-trace-api#customizing-stack-traces

Inherited from

Error.prepareStackTrace