Add esm build configuration and package.json exports (#201)

This will build a cjs compatible bundle and an esm compatible bundle and package them both, allowing downstream projects to import the module type that fits their project.

package.json

@@ -17,10 +17,20 @@
         "type": "git",
         "url": "https://github.com/jscheiny/safe-units.git"
     },
-    "main": "dist/src/index.js",
-    "typings": "dist/src/index.d.ts",
+    "main": "./dist/cjs/index.js",
+    "module": "./dist/esm/index.js",
+    "types": "./dist/types/index.d.ts",
+    "exports": {
+        "import": "./dist/esm/index.js",
+        "require": "./dist/cjs/index.js"
+    },
+    "files": [
+        "dist"
+    ],
     "scripts": {
-        "build": "tsc -p src",
+        "build:cjs": "tsc -p tsconfig.cjs.json && echo '{\"type\":\"commonjs\"}' > dist/cjs/package.json",
+        "build:esm": "tsc -p tsconfig.esm.json && echo '{\"type\":\"module\"}' > dist/esm/package.json",
+        "build": "yarn run build:cjs && yarn run build:esm",
         "clean": "rimraf dist docs/build",
         "compile:docs": "tsc -p docsgen",
         "compile:examples": "tsc -p docs/examples",

tsconfig.base.json

@@ -1,7 +1,8 @@
 {
     "compilerOptions": {
-        "module": "commonjs",
         "moduleResolution": "node",
+        "declaration": true,
+        "declarationDir": "./dist/types",
         "noFallthroughCasesInSwitch": true,
         "noImplicitAny": true,
         "noImplicitReturns": true,
@@ -18,5 +19,13 @@
             "es2015",
             "es2015.core"
         ]
-    }
+    },
+    "include": [
+        "src"
+    ],
+    "exclude": [
+        "dist",
+        "node_modules",
+        "test"
+    ]
 }

tsconfig.cjs.json

@@ -0,0 +1,8 @@
+{
+    "extends": "./tsconfig.base.json",
+    "compilerOptions": {
+        "module": "commonjs",
+        "outDir": "./dist/cjs",
+        "target": "ES2015"
+    }
+}

tsconfig.esm.json

@@ -0,0 +1,8 @@
+{
+    "extends": "./tsconfig.base.json",
+    "compilerOptions": {
+        "module": "es6",
+        "outDir": "./dist/esm",
+        "target": "es6"
+    }
+}