feat: add esm support

README.md

@@ -137,10 +137,6 @@ The example shown above is used as the default values, you only need to specify
 
 ## `StrfDate` Reference
 
-### Codes
-
-A flag lets you modify the output of a code used in your format. Here are the default flags used for both `StrfDate` and `ExpressDate`:
-
 | Code    | Description                                                         |
 | ------- | ------------------------------------------------------------------- |
 | `%%`    | a literal %                                                         |

build.mjs

@@ -0,0 +1,17 @@
+import {execSync} from 'child_process';
+import {rmSync, mkdirSync, renameSync, copyFileSync, rmdirSync} from 'fs';
+
+rmSync('dist', {force: true, recursive: true});
+mkdirSync('dist');
+
+mkdirSync('dist/ts');
+execSync('tsc --module CommonJS');
+renameSync('dist/ts/index.js', 'dist/index.js');
+execSync('tsc --module ESNext');
+renameSync('dist/ts/index.js', 'dist/index.mjs');
+renameSync('dist/ts/index.d.ts', 'dist/index.d.ts');
+rmdirSync('dist/ts');
+
+for (const file of ['package.json', 'README.md', 'LICENSE']) {
+  copyFileSync(file, 'dist/' + file);
+}