babel-plugin-tcomb

0.4.0 verified Sat Apr 25 auth: no javascript abandoned

Babel plugin that adds runtime type checking from Flow annotations using tcomb. Version 0.4.0, released 2020-09-05. This is the latest stable release; prior versions support Babel 6, latest supports Babel 7. Transforms Flow type annotations into runtime assertions via tcomb. Different from flow-remove-types or babel-plugin-transform-flow-strip-types because it keeps the type information for runtime validation. Works alongside Flow for hybrid static + dynamic checking. Supports refinement types, immutability enforcement, and IO boundary validation. Abandoned as of November 2021; no commits or releases since 0.4.0.

Common errors

error Error: Cannot find module 'tcomb' ↓

cause tcomb is a peer dependency and not installed automatically.

fix

npm install --save-dev tcomb

error TypeError: [tcomb] Invalid value "x" supplied to b: Number ↓

cause Runtime type check failed – argument type mismatch.

fix

Correct the call to pass a number: sum(1, 2);

error Error: Plugin 0 specified in "..." provided an invalid property of type "..." ↓

cause Plugin order or misconfiguration in .babelrc.

fix

Ensure plugins array contains 'tcomb' after 'syntax-flow' and before 'transform-flow-strip-types'. Try passPerPreset: true.

error ReferenceError: t is not defined ↓

cause tcomb not imported or requireable in your source module.

fix

Add import t from 'tcomb' at the top of your file, or ensure CommonJS require('tcomb') works.

Warnings

breaking Version 0.4.0 requires Babel 7; incompatible with Babel 6 projects. ↓

fix Upgrade to Babel 7 or pin to 0.3.27 for Babel 6.

deprecated Package is no longer maintained; last release 0.4.0 (2020). No bug fixes or updates for newer Babel versions. ↓

fix Consider alternatives like babel-plugin-runtime-typecheck or TypeScript with ttypescript.

gotcha tcomb must be requireable at runtime; if using ES modules, ensure transform-modules-commonjs or similar is applied before tcomb plugin. ↓

fix Add plugin order: transform-modules-commonjs before tcomb, or use Babel env with modules: 'commonjs'.

gotcha Passing passPerPreset: true may be required when using multiple presets to avoid conflicts. ↓

fix Set passPerPreset: true in .babelrc.

breaking Removed support for Babel 6 in v0.4.0; no migration path for Babel 6 projects. ↓

fix Stick with v0.3.27 for Babel 6, or upgrade entire project to Babel 7.

Install

npm install babel-plugin-tcomb

yarn add babel-plugin-tcomb

pnpm add babel-plugin-tcomb

Imports

default
```
// .babelrc
{
  "plugins": ["tcomb"]
}
```
The plugin is used as a Babel plugin, not imported directly in source code.
tcomb
wrong
```
import { t } from 'tcomb'
```
correct
```
import t from 'tcomb'
```
tcomb is a CommonJS module with default export; ES6 default import works with Babel.
Flow type annotations
wrong
```
function add(a, b) { return a + b; }
```
correct
```
function add(a: number, b: number): number { return a + b; }
```
Without annotations, no runtime checks are generated. Annotations must be Flow-standard.

Quickstart

Shows Babel setup and runtime type checking triggered by a Flow-annotated function call with a type mismatch.

// .babelrc
{
  "plugins": [
    "syntax-flow",
    "tcomb",
    "transform-flow-strip-types"
  ]
}

// src/index.js
function sum(a: number, b: number): number {
  return a + b;
}

// This will throw at runtime:
sum(1, 'x'); // Uncaught TypeError: [tcomb] Invalid value "x" supplied to b: Number