How to use the systemjs.defaultJSExtensions function in systemjs

// combine kernel modules and compile

"use strict";
let fs = require("fs");
let path = require("path");
let childProcess = require("child_process");
let System = require('systemjs');
System.defaultJSExtensions = true;

// let modules = [
//     "./src/turbo/common.tts",
//     "./src/tracer/axis.tts",
//     "./src/turbo/color.tts",
//     "./src/turbo/vector.tts",
//     "./src/utils/util.tts",
//     "./src/turbo/box.tts",
//     "./src/turbo/matrix.tts",
//     "./src/turbo/image.tts",
//     "./src/turbo/texture.tts",
//     "./src/turbo/material.tts",
//     "./src/tracer/ray.tts",
//
//     "./src/turbo/shapes/shape.tts",
//     "./src/turbo/shapes/cube.tts",
//     "./src/turbo/shapes/sphere.tts",
//     "./src/turbo/shapes/triangle.tts",
//     "./src/turbo/shapes/mesh.tts",
//
//     "./src/turbo/tree.tts",
//     "./src/tracer/hit.tts",
//     "./src/turbo/camera.tts",
//     "./src/turbo/scene.tts",
//     "./src/three/buffer_geometry.tts",
//     "./src/tracer/sampler.tts",
//
//     "./src/tracer/vector3.tts",
//     "./src/tracer/color3.tts",
//     "./src/tracer/matrix4.tts",
//
// ];
let modules = [
    "./src/turbo/vector3.tbs",
    "./src/turbo/color.tbs",
    "./src/turbo/image.tbs"
];
let buildCommand = [];
modules.forEach((file) => {
    buildCommand.push(path.resolve(__dirname, file));
});

let TURBO_PATH = path.resolve(__dirname, "../");
process.env.TURBO_PATH = TURBO_PATH;

// let outFile = path.resolve(__dirname, "xray-kernel-turbo.asm.js");
let outFile = path.resolve(__dirname, "xray-kernel-turbo");