Add ESM build

.gitignore

@@ -1,41 +1,56 @@
-*.js
-*.d.ts
-*.map
+.DS_Store
+dist/
+coverage/
+docs/
 
 # Logs
 logs
 *.log
 npm-debug.log*
 yarn-debug.log*
 yarn-error.log*
+lerna-debug.log*
+
+# Diagnostic reports (https://nodejs.org/api/report.html)
+report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json
 
 # Runtime data
 pids
 *.pid
 *.seed
 *.pid.lock
 
-# Directory for instrumented libs generated by jscoverage/JSCover
-lib-cov
-
 # Coverage directory used by tools like istanbul
 coverage
+*.lcov
 
 # nyc test coverage
 .nyc_output
 
+# node-waf configuration
+.lock-wscript
+
+# Compiled binary addons (https://nodejs.org/api/addons.html)
+build/Release
+
 # Dependency directories
 node_modules/
 
-# TypeScript v1 declaration files
-typings/
+# TypeScript cache
+*.tsbuildinfo
 
 # Optional npm cache directory
 .npm
 
 # Optional eslint cache
 .eslintcache
 
+# Microbundle cache
+.rpt2_cache/
+.rts2_cache_cjs/
+.rts2_cache_es/
+.rts2_cache_umd/
+
 # Optional REPL history
 .node_repl_history
 
@@ -47,49 +62,17 @@ typings/
 
 # dotenv environment variables file
 .env
-
-# parcel-bundler cache (https://parceljs.org/)
-.cache
-
-# next.js build output
-.next
-
-# nuxt.js build output
-.nuxt
-
-# vuepress build output
-.vuepress/dist
-
-# Serverless directories
-.serverless
-
-### OSX ###
-# General
-.DS_Store
-.AppleDouble
-.LSOverride
-
-# Icon must end with two \r
-Icon
-
-# Thumbnails
-._*
-
-# Files that might appear in the root of a volume
-.DocumentRevisions-V100
-.fseventsd
-.Spotlight-V100
-.TemporaryItems
-.Trashes
-.VolumeIcon.icns
-.com.apple.timemachine.donotpresent
-
-# Directories potentially created on remote AFP share
-.AppleDB
-.AppleDesktop
-Network Trash Folder
-Temporary Items
-.apdisk
-
-
-# End of https://www.gitignore.io/api/osx,node
+.env.test
+
+# Stores VSCode versions used for testing VSCode extensions
+.vscode-test
+
+# yarn v3 (w/o zero-install)
+# See: https://yarnpkg.com/getting-started/qa#which-files-should-be-gitignored
+.pnp.*
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/sdks
+!.yarn/versions

.nvmrc

@@ -1 +1 @@
-v12
+lts/*

package.json

@@ -2,15 +2,28 @@
   "name": "@metamask/safe-event-emitter",
   "version": "3.0.0",
   "description": "An EventEmitter that isolates the emitter from errors in handlers",
-  "main": "index.js",
+  "main": "dist/cjs/index.js",
+  "module": "dist/esm/index.js",
+  "types": "dist/cjs/index.d.ts",
+  "exports": {
+    ".": {
+      "import": {
+        "types": "./dist/esm/index.d.ts",
+        "default": "./dist/esm/index.mjs"
+      },
+      "require": {
+        "types": "./dist/cjs/index.d.ts",
+        "default": "./dist/cjs/index.js"
+      }
+    },
+    "./package.json": "./package.json"
+  },
   "publishConfig": {
     "registry": "https://registry.npmjs.org/",
     "access": "public"
   },
   "files": [
-    "index.js",
-    "index.d.ts",
-    "index.js.map"
+    "dist"
   ],
   "repository": {
     "type": "git",
@@ -21,7 +34,10 @@
   },
   "scripts": {
     "prepublishOnly": "yarn build",
-    "build": "tsc --project .",
+    "build": "yarn build:cjs && yarn build:esm",
+    "build:cjs": "tsc --project .",
+    "build:esm": "tsc --project tsconfig.esm.json && yarn build:esm:rename",
+    "build:esm:rename": "./scripts/rename-esm.sh",
     "test": "jest",
     "lint": "eslint . --ext .ts,.js"
   },

scripts/rename-esm.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+
+set -e
+set -u
+set -o pipefail
+
+if [[ ${RUNNER_DEBUG:-0} == 1 ]]; then
+  set -x
+fi
+
+for file in dist/esm/*.js; do
+  mv "$file" "${file%.js}.mjs"
+done

tsconfig.esm.json

@@ -0,0 +1,14 @@
+{
+  "compilerOptions": {
+    "declaration": true,
+    "module": "ES6",
+    "moduleResolution": "Node",
+    "outDir": "dist/esm",
+    "sourceMap": true,
+    "strict": true,
+    "target": "ES2017"
+  },
+  "include": [
+    "./**/*.ts"
+  ]
+}

tsconfig.json

@@ -2,6 +2,7 @@
   "compilerOptions": {
     "declaration": true,
     "module": "CommonJS",
+    "outDir": "dist/cjs",
     "sourceMap": true,
     "strict": true,
     "target": "ES2017"