Only sort keys on objects

Fixes #20.

Author: kevva

index.js

@@ -6,6 +6,7 @@ const sortKeys = require('sort-keys');
 const makeDir = require('make-dir');
 const pify = require('pify');
 const detectIndent = require('detect-indent');
+const isPlainObj = require('is-plain-obj');
 
 const init = (fn, filePath, data, options) => {
 	if (!filePath) {
@@ -21,7 +22,7 @@ const init = (fn, filePath, data, options) => {
 		sortKeys: false
 	}, options);
 
-	if (options.sortKeys) {
+	if (options.sortKeys && isPlainObj(data)) {
 		data = sortKeys(data, {
 			deep: true,
 			compare: typeof options.sortKeys === 'function' ? options.sortKeys : undefined

package.json

@@ -36,6 +36,7 @@
 	"dependencies": {
 		"detect-indent": "^5.0.0",
 		"graceful-fs": "^4.1.2",
+		"is-plain-obj": "^1.1.0",
 		"make-dir": "^1.0.0",
 		"pify": "^4.0.0",
 		"sort-keys": "^2.0.0",

test.js

@@ -40,6 +40,8 @@ test('async - {sortKeys: true}', async t => {
 	const tmp = path.join(tempfile(), 'foo');
 	await m(tmp, {c: true, b: true, a: true}, {sortKeys: true});
 	t.is(fs.readFileSync(tmp, 'utf8'), '{\n\t"a": true,\n\t"b": true,\n\t"c": true\n}\n');
+	await m(tmp, ['a', 'b', 'c'], {sortKeys: true});
+	t.is(fs.readFileSync(tmp, 'utf8'), '[\n\t"a",\n\t"b",\n\t"c"\n]\n');
 });
 
 test('async - {sortKeys: false}', async t => {