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TeaScript is an experimental transformation tool that adds type annotations, ES2015, React, and what not, to JavaScript. It can be integrated into an editor, saving plain old JavaScript with annotations to disk. This makes it so that it doesn't need a special compile step and toolchain setup, and plays nicely with other tools such as debuggers.

For example, when your editor shows JavaScript with type annotations

function repeat(s : string, n : number) : void {
    return // ... 

on disk it will actually look like:

function repeat(s /*: string*/, n /*: number*/) /*: void*/ {
    return // ... 

TeaScript simply turns all JavaScript extensions into annotations in comments, and can translate it back to the original form on the fly. This way, editors always see the extended version and can provide better code completion and what not. And build tools, debuggers, packagers, etc. still work since they see pure JavaScript.

TeaScript can be used for small transformations like getting rid of type annotations, but in principle can be used together with any transformation. For example, teascript -c --es6 can compile ES6 with classes

class Foo {
    constructor(foo, bar) { = foo; = bar;
    getFoo() {
        return foo;

into legal ES5 code with annotations in comments:

/*+class Foo {*/
/**+constructor(foo, bar) {*/function Foo(foo, bar) {"use strict"; = foo; = bar;
/**+getFoo() {*/Object.defineProperty(Foo.prototype,"getFoo",{writable:true,configurable:true,value:function() {"use strict";
        return foo;

Command-line Use

Output plain JavaScript for a file:

teascript -c simple.js

Output ES5 for an ES6 file:

teascript -c --es6 simple.js

Restore extended JavaScript from stdin:

echo "function foo() /*: void*/ {}" | teascript -d

Output plain JavaScript for a React module:

teascript --react -c react.jsx