transp

Transparent client-side transpilation

<script src="https://cdn.jsdelivr.net/npm/transp@0.0.2/dist/transp.min.js"></script>
<trans-script>
    // This is Typescript!
    console.log('Hello World' as string)
</trans-script>

Overview

Transp enables standalone client-side transparent 0transpilation (Typescript, JSX, etc.), without requiring node.js It uses Babel Standalone to transpile, and handles the details needed for importing scripts.

It aims to be the closest thing possible to "Typescript working natively in the browser".

Purpose

This library is not meant for production, as it generates a huge package. This is also the case for babel-standalone. It's meant to enable an easier development/setup/debugging, or to be part of a bigger developer-facing solution.

How to Use

transp is meant for use in a browser enviornment. It provides a JavaScript API and an HTML custom element.

Install

npm install transp

Use as a JavaScript API

The JavaScript API provides the following functions:

import(href: string): Promise<any>

A drop-in replacement for dynamic import, which transpiles the required resources, resolves inner imports, and returns a promise with the resolved and evaluated model. Example:

<script>
    import('some-typescript-module.ts').then(module => doSomethingWithModule)
</script>

eval(code: string): Promise<any>

Almost a drop-in replacement for eval, with two differences:

• The code can be Typescript (or anything supported by the Babel configuration)
• The code is evaluated asynchronously, and the return value is a promise that will resolve to the result of the code.

configure

The default import and eval functions provided by the library use the default configuration. To override the defaults, for example by enabling

Use as an HTML Custom Element

To enable the custom element, the library exposes a function: initCustomElement(enviornment = transp, name = 'trans-script')

The custom element is replacement for an HTML script element, and can be used with src or with an inline script.

Unlike regular script elements, The trans-script element is never executed synchrnously.

The following:

    <trans-script>
        import {hello} from './hello'
        // Typescript!
        console.log(hello() as string)
    </trans-script>

... is equivalent to a <script async> element with a transpiled version of the internal code.

Custom Configurations

The default eval and import functionality uses a default set of Babel presets. To override those, use the configure function:

import {configure, initCustomElement} from 'transp'
interface LibConfig {
    version: string
    url: string
    global: string | null
}

export interface Config {
    presets: string[]
    plugins: string[]
    extensions: string[]
    sourcemaps: 'inline' | 'external' | 'none'
    libraries: {[name: string]: LibConfig}
    baseURL: string
    enableLibraryLinks: boolean
}

const myTransp = configure({
    presets: ['jsx', 'typescript', ...], // Babel presets. Default: ['typescript']
    plugins: [], // Babel plugins. Default: empty
    extensions: ['ts', 'js', 'jsx'], // supported file extensions. Default: ['js', 'ts']
    sourcemaps: 'inline' | 'external | 'none', // default: inline
    libraries: {
        lodash: {'4.17.20', url: 'https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.20/lodash.min.js', global: '_'}
    }, // Importable named libraries
    baseURL: 'http://example.com', // base URL for links. Default is document URL
    enableLibraryLinks: true // Enable searching dependencies in <link rel="library">
})

myTransp.import('some-file.ts').then(...)
initCustomElement(myTransp, 'my-script')

Loading External Dependencies

A transpiled script may references an external dependency, for example: import {map} from 'lodash'

To resolve external dependencies, the modules have to be defined either in the configuration passed to the configure function, or in link tags with the following scheme:

<link rel="library" name="{module name}" href="{the library URL}" global={the name of the global variable exposed by the library} />