rtts_assert

2.0.0-alpha.37 verified Fri May 01 auth: no javascript maintenance

A run-time type assertion library for JavaScript, used internally by Angular for runtime type checks. Current stable version is 2.0.0-alpha.37 (pre-release, adapted from v0.1.0 originally designed for Traceur). No regular release cadence—packaged within Angular monorepo. Key differentiator: provides runtime type checking akin to TypeScript's emitDecoratorMetadata, useful in testing and dynamic type validation. Lightweight with no runtime dependencies.

Common errors

error TypeError: assert.argumentTypes is not a function ↓

cause assert.argumentTypes was removed in v2.0.0.

fix

Replace with assert.type(arg1, Type), assert.type(arg2, Type), etc.

error Error: Expected argument to be a string but got 'undefined' ↓

cause assert.define first argument must be a string name, not a type reference.

fix

assert.define('MyType', ..., not assert.define(MyType, ...).

error AssertionError: Expected String, got Number. ↓

cause Value does not match the asserted type.

fix

Check the value and type: assert.type(value, ActualType).

Warnings

breaking assert.argumentTypes is deprecated and removed in v2; use assert.type instead. ↓

fix Replace assert.argumentTypes(arg1, Type, arg2, Type) with individual assert.type calls.

deprecated ES5 build script es5build.js is no longer maintained. ↓

fix Use a modern bundler (e.g., esbuild, Webpack) to transpile ES6 sources.

gotcha assert(value).is(...) returns an assertion object, not a boolean; must be called as a statement. ↓

fix Do not assign the result: use assert(value).is(Type) without assignment.

gotcha Custom types defined with assert.define must use a string name; using a class name will silently fail. ↓

fix assert.define('MyClass', fn) instead of assert.define(MyClass, fn).

breaking Predefined types like assert.string now require assert.type(value, assert.string) instead of assert(value).is(assert.string) pattern changed. ↓

fix Use assert.type(value, assert.string) or assert(value).is(assert.string) still works.

Install

npm install rtts_assert

yarn add rtts_assert

pnpm add rtts_assert

Imports

assert

wrong

const assert = require('rtts_assert');

correct

import { assert } from 'rtts_assert';

ESM-only since v2; no CommonJS support.

assert.type
wrong
```
assert(value, Type);
```
correct
```
assert.type(value, Type);
```
assert.type requires two args; direct assert() with one arg is different (returns an assertion object).

assert.define

wrong

assert.define(MyType, function(value) { ... });

correct

assert.define('MyType', function(value) { ... });

First argument must be a string name, not a class/function.

Quickstart

Shows basic type assertion, value assertion, and custom type definition.

import { assert } from 'rtts_assert';

assert.type('hello', String); // passes
assert.type(42, String); // throws: Expected String, got Number.

const value = 'test';
assert(value).is(String); // passes
assert(value).is(Number); // throws

assert.define('Email', function(value) {
  assert(value).is(String);
  if (value.indexOf('@') === -1) {
    assert.fail('must contain @');
  }
});

assert.type('user@example.com', Email); // passes
assert.type('invalid', Email); // throws: must contain @