add esm bundle

build.js

@@ -0,0 +1,54 @@
+#!/usr/bin/env node
+"use strict";
+
+var fs = require("fs");
+var browserify = require("browserify");
+var timers = require("./src/fake-timers-src.js");
+
+function makeBundle(entryPoint, config, done) {
+    browserify(entryPoint, config).bundle(function(err, buffer) {
+        if (err) {
+            throw err;
+        }
+        done(buffer.toString());
+    });
+}
+
+makeBundle(
+    "./src/fake-timers-src.js",
+    {
+        standalone: "FakeTimers",
+        detectGlobals: false
+    },
+    function(bundle) {
+        fs.writeFileSync("fake-timers.js", bundle);
+    }
+);
+
+makeBundle(
+    "./src/fake-timers-esm.js",
+    {
+        detectGlobals: false
+    },
+    function(bundle) {
+        var source = "let FakeTimers;\n";
+        source += bundle;
+        source += Object.keys(timers)
+            .map(function(key) {
+                return (
+                    "const _" +
+                    key +
+                    " = FakeTimers." +
+                    key +
+                    "\nexport { _" +
+                    key +
+                    " as " +
+                    key +
+                    " };"
+                );
+            })
+            .join("\n");
+
+        fs.writeFileSync("fake-timers-esm.js", source);
+    }
+);