Babylon.js/Tools/Gulp/tasks/gulpTasks-watch.js

// Import Dependencies.
var gulp = require("gulp");
var webpack = require('webpack');
var webpackStream = require("webpack-stream");
var debug = require("gulp-debug");

// Read the full config.
var config = require("../config.json");

/**
 * Watch ts files from typescript .
 * Hack into the cli :-)
 */
gulp.task("srcTscWatch", function() {
    // Reuse The TSC CLI from gulp to enable -w.
    process.argv[2] = "-w";
    process.argv[3] = "-p";
    process.argv[4] = "../../src/tsconfig.json";
    require("../../../node_modules/typescript/lib/tsc.js");
    return Promise.resolve();
});

/**
 * Watch ts files and fire repective tasks.
 */
gulp.task("watch", gulp.series("srcTscWatch", function startWatch() {
    var tasks = [];

    config.modules.map(function(module) {
        if (config[module].build && config[module].build.webpack) {
            for (var index = 0; index < config[module].libraries.length; index++) {
                var library = config[module].libraries[index];
                if (library.preventLoadLibrary) { 
                    continue;
                }

                let wpconfig = require(config[module].build.webpack);
                // watch on.
                wpconfig.watch = true;
                // dev mode and absolute path sourcemaps for debugging
                wpconfig.mode = "development";
                wpconfig.output.devtoolModuleFilenameTemplate = "[absolute-resource-path]";
                //config.stats = "minimal";

                var outputDirectory = config.build.tempDirectory + config[module].build.distOutputDirectory;
                tasks.push(webpackStream(wpconfig, webpack).pipe(gulp.dest(outputDirectory)))
            }
        }
    });

    return Promise.resolve();
}));