build esm module that can be imported from browsers.

closes https://github.com/fiatjaf/nostr-tools/issues/14

build.js

@@ -0,0 +1,25 @@
+#!/usr/bin/env node
+
+const esbuild = require('esbuild')
+const alias = require('esbuild-plugin-alias')
+const nodeGlobals = require('@esbuild-plugins/node-globals-polyfill').default
+
+const buildOptions = {
+  entryPoints: ['index.js'],
+  outfile: 'nostr.js',
+  bundle: true,
+  format: 'esm',
+  plugins: [
+    alias({
+      stream: require.resolve('readable-stream')
+    }),
+    nodeGlobals({buffer: true})
+  ],
+  define: {
+    window: 'self',
+    global: 'self'
+  },
+  loader: {'.js': 'jsx'}
+}
+
+esbuild.build(buildOptions).then(() => console.log('build success.'))