feat(outputFileSync): implements mergeContent

src/utils.ts

@@ -1,15 +1,40 @@
 import * as fs from 'node:fs'
 import type { WriteFileOptions } from 'node:fs'
+import { Buffer } from 'node:buffer'
 import path from 'pathe'
+import { defu } from 'defu'
 
 export function outputFileSync(
   filepath: string,
   data: string | NodeJS.ArrayBufferView,
-  options?: WriteFileOptions,
+  options?: WriteFileOptions & {
+    /**
+     * Perform a json deep merge if file already exists
+     * Explicitly set to `true` if you want to perform a simple concatenate for other file types
+     */
+    mergeContent?: boolean | 'json'
+  },
 ) {
+  // Ensure directory exists
   const dir = path.dirname(filepath)
   if (!fs.existsSync(dir))
     fs.mkdirSync(dir, { recursive: true })
 
+  // Perform mergeContent
+  if (options?.mergeContent && fs.existsSync(filepath)) {
+    // special deep merger for json
+    if (filepath.endsWith('.json')) {
+      if (typeof data !== 'string')
+        throw new Error('Please provide `data` as a JSON stringified object')
+
+      data = JSON.stringify(defu(JSON.parse(data), JSON.parse(fs.readFileSync(filepath).toString())), undefined, 2)
+    }
+    // simple concat for other files
+    else if (options.mergeContent === true) {
+      data = Buffer.concat([fs.readFileSync(filepath), new Uint8Array(Buffer.from('Hello Node.js'))])
+    }
+  }
+
+  // Write the file
   fs.writeFileSync(filepath, data, options)
 }