gulpfile.js

var gulp = require("gulp");
var watchify = require("watchify");
var browserify = require("browserify");
var tsify = require("tsify");
var source = require("vinyl-source-stream");

gulp.task("watchify-tsify", function() {
  var b = watchify(browserify({
    entries: [ "./ts/a.ts", "./ts/b.ts", /* ... */],
    cache: {},
    packageCache: {}
  }));
  
  function runBundle() {
    return b.plugin(tsify, {
      noImplicitAny: true,
      target: "es5"
    }).bundle().pipe(source("./all.js")).pipe(gulp.dest("./js/"));
  }
  
  b.on("update", runBundle);
  b.on("log", function(msg) {
    console.log(msg);
  });
  bundle();
});