support esm

package.json

@@ -4,6 +4,7 @@
   "description": "JavaScript client SDK for bidirectional communication with Centrifugo and Centrifuge-based server from browser, NodeJS and React Native",
   "main": "build/index.js",
   "types": "build/index.d.ts",
+  "module": "build/esm/index.js",
   "files": [
     "dist/**",
     "build/**"
@@ -18,8 +19,10 @@
     "clean": "rm -rf dist build package",
     "ts-node": "ts-node",
     "docs": "typedoc --exclude '**/transport_*.ts' --exclude '**/*.test.ts' --exclude '**/*+(utils|json|codes|browser).ts' --excludePrivate --excludeInternal --entryPoints src/*.ts",
-    "build": "tsc -p tsconfig.json",
-    "build-all": "yarn clean && yarn build && yarn build-browser && yarn build-browser-protobuf",
+    "build:cjs": "tsc -p tsconfig.cjs.json",
+    "build:esm": "tsc -p tsconfig.esm.json",
+    "build": "yarn build:cjs && yarn build:esm",
+    "build-all": "yarn clean && yarn build:cjs && yarn build:esm && yarn build-browser && yarn build-browser-protobuf",
     "build-browser": "esbuild src/browser.ts --bundle --minify --sourcemap --outfile=dist/centrifuge.js",
     "dev": "esbuild src/browser.ts --bundle --outfile=dist/centrifuge.js --servedir=dist/ --serve=2000",
     "build-browser-protobuf": "esbuild src/protobuf/browser.ts --bundle --minify --sourcemap --outfile=dist/centrifuge.protobuf.js",

tsconfig.esm.json

@@ -0,0 +1,42 @@
+{
+  "compilerOptions": {
+    "target": "es6",
+    "module": "ESNext",
+    "moduleResolution": "node",
+    "declaration": true,
+    "strict": true,
+    "noImplicitAny": false /* Raise error on expressions and declarations with an implied 'any' type. */,
+    "strictNullChecks": true /* Enable strict null checks. */,
+    "strictFunctionTypes": true /* Enable strict checking of function types. */,
+    "noUnusedLocals": true /* Report errors on unused locals. */,
+    "noUnusedParameters": true /* Report errors on unused parameters. */,
+    "noImplicitReturns": true /* Report error when not all code paths in function return a value. */,
+    "noFallthroughCasesInSwitch": true /* Report errors for fallthrough cases in switch statement. */,
+    "importHelpers": false, /* https://github.com/centrifugal/centrifuge-js/issues/193 */
+    "skipLibCheck": true,
+    "esModuleInterop": true,
+    "allowSyntheticDefaultImports": true,
+    "experimentalDecorators": true,
+    "resolveJsonModule": true,
+    "sourceMap": true,
+    "stripInternal": true,
+    "outDir": "./build/esm",
+    "types": [
+      "node",
+      "jest"
+    ],
+    "lib": [
+      "ES6",
+      "DOM"
+    ]
+  },
+  "include": [
+    "src/**/*.ts",
+    "src/**/*.json"
+  ],
+  "exclude": [
+    "node_modules",
+    "**/*.test.ts",
+    "**/browser.ts"
+  ]
+}