Transpilers, Babel and TypeScript

JavaScript transpilers (or transcompilers) are tools that convert a specific language code into ES JavaScript. It takes the source code of a program written in one programming language as its input and produces the equivalent source code in another programming language.

Clarive supports using transpilers to filter and preprocess JS code before being executed. Clarive also ships with a few transpilers pre-installed:

  • Babel (ES2015)
  • TypeScript

Using Transpilers

To have your code processed through one of the installed transpilers use a special JavaScript pragma created for this.

The pragma to activate transpiling is this:

    "use transpiler([transpiler name])";

This will have the full current body of source code transpiled, independently of where the pragma is declared.

Notice that althought transpiling is not a very expensive operation, everytime new unique source code is created, it has to be transpiled, which means loading the transpiler, parsing and converting to JavaScript. Clarive caches the transpiled code, so the next execution will only cost the same as if it were written in plain JavaScript, which can mean a 100x or more improvement in execution speed.

If you believe you're having issues with transpiled code cached, try wiping the cache to force it to be transpiled again.


Babel allows you to use the latest developments in the EcmaScript standard (ie. ES6) in the Clarive JS VM, which conforms up to ES5.

"use transpiler(babel)";

// Expression bodies
evens = [2,4,6,8]
var odds = => v + 1);
var nums =, i) => v + i);

// Interpolate variable bindings
var name = "Bob", time = "today";
print(`Hello ${name}, how are you ${time}?`);

class Animal {
    constructor(name, voice) { = name;
        this.voice = voice;

        this._eyes = 2;
    get eyes() {
        return this._eyes;
    speak() {
        console.log(`The ${} says ${this.voice}.`);

var foo = new Animal('dog', 'woof');
foo.speak(); // The dog says woof.

For more information, checkout the Babel documentation at


TypeScript is a strict superset of JavaScript, and adds optional static typing and class-based object-oriented programming to the language

"use transpiler(typescript)";

class Greeter {
    greeting: string;
    constructor(message: string) {
        this.greeting = message;
    greet() {
        return "Hello, " + this.greeting;

let greeter = new Greeter("world");
print( greeter.greet() );

For more information:

Creating Transpilers

Transpilers can be created as part of a plugin, by adding a special procesor anonymous function to the [plugin]/transpiler/ folder.

For creating a transpiler from a standard transpiler library, it is recommended you install first the library in [plugin]/modules/, then write a lightweight transpiler that require()s the library.

This is the transpiler procesor skelleton, ie [plugin]/transpiler/mytranspiler.js:

module.exports = function(code){
    var tr = require('../transpiler/mytranspiler-lib.js');
    return tr.transpile(code);

The anonymous function receives code as an argument, which is the full body of the pre-transpiled code.

The function must return a string with the transpiled code.

Now, we can use it in our Clarive JS DSL:

"use transpiler(mytranspiler)";

// .. my pre-transpiled code ..