Briklab Docs

Getting Started with JSTC ​

JSTC (JavaScript Type Checker) provides runtime type validation with configurable protection levels.

What is JSTC? ​

JSTC validates JavaScript values at runtime against type specifications. Unlike TypeScript, which validates at compile-time, JSTC checks values while your code is running.

ts
import JSTC from "@briklab/lib/jstc";

// Validate a single value (wrap in array for .for())
const isNumber = JSTC.for([42]).check(["number"]);
console.log(isNumber); // true

// Validate multiple values with matching types
const mixedValid = JSTC.for([42, "hello", true]).check(["number", "string", "boolean"]);
console.log(mixedValid); // true

Basic Usage ​

Using the JSTC Singleton ​

The easiest way to get started is using the JSTC constant:

ts
import JSTC from "@briklab/lib/jstc";

JSTC.setProtectionLevel("boundary");

// Check if values match the given types (in order)
const isValid = JSTC.for([42, "hello", 3.14]).check(["number", "string", "number"]);
console.log(isValid); // true - values match type specifications

Creating Custom Instances ​

For more control, create a JSTypeChecker instance:

ts
import { JSTypeChecker } from "@briklab/lib/jstc";

const checker = new JSTypeChecker("hardened");
const result = checker.for([null]).check(["null"]);
console.log(result); // true

Live Demo ​

Recommended to test it in your browser. The test here might not work properly
Console
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Supported Types ​

JSTC supports the following type names:

  • "number" - Any number (integer or float)
  • "string" - Text values
  • "boolean" - True or false
  • "object" - Objects (not arrays or null)
  • "array" - Array values
  • "function" - Function values
  • "symbol" - Symbol values
  • "bigint" - BigInt values
  • "undefined" - Undefined values
  • "null" - Null values

Protection Levels ​

Protection levels control runtime safety behavior:

  • "none": No protection checks or warnings
  • "boundary": Balanced safety with warning-based guidance
  • "hardened": Defensive mode that throws on invalid usage
  • "sandbox": Boundary behavior plus richer hints
ts
JSTC.setProtectionLevel("hardened");
// Now JSTC validation runs in hardened mode

Next Steps ​

Learn more about JSTC: