Fix preserving leading underscores and dollar signs

Fixes #80

Author: sindresorhus

index.js

@@ -93,14 +93,16 @@ const transform = (input, options = {}, isSeen = new WeakMap(), parentPath) => {
 			if (cache.has(cacheKey)) {
 				key = cache.get(cacheKey);
 			} else {
-				const returnValue = camelCase(key, {pascalCase, locale: false, preserveConsecutiveUppercase});
+				// Preserve leading `_` and `$` as they typically have semantic meaning
+				// This should eventually be fixed in the `camelcase` package itself
+				const leadingPrefix = key.match(/^[_$]*/)[0];
+				const transformed = camelCase(key.slice(leadingPrefix.length), {pascalCase, locale: false, preserveConsecutiveUppercase});
+				key = leadingPrefix + transformed;
 
 				// Only cache reasonable length keys to prevent memory abuse
 				if (key.length < 100) {
-					cache.set(cacheKey, returnValue);
+					cache.set(cacheKey, key);
 				}
-
-				key = returnValue;
 			}
 		}
 

readme.md

@@ -33,6 +33,13 @@ camelcaseKeys(commandLineArguments);
 //=> {_: [], fooBar: true}
 ```
 
+Leading `_` and `$` are preserved as they have semantic meaning.
+
+```js
+camelcaseKeys({_foo_bar: true, $baz_qux: true});
+//=> {_fooBar: true, $bazQux: true}
+```
+
 ## API
 
 ### camelcaseKeys(input, options?)

test.js

@@ -378,6 +378,64 @@ test('preserve numeric string keys', t => {
 	t.deepEqual(camelcaseKeys([{'4.2': 'foo'}, {42: 'bar'}]), [{'4.2': 'foo'}, {42: 'bar'}]);
 });
 
+test('preserve leading underscores and dollar signs', t => {
+	// Single leading underscore
+	t.deepEqual(camelcaseKeys({_name: true}), {_name: true});
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({_name_obj: 'value'}), {_nameObj: 'value'});
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({_foo_bar: true}), {_fooBar: true});
+
+	// Single leading dollar sign
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({$foo_bar: true}), {$fooBar: true});
+	t.deepEqual(camelcaseKeys({$element: true}), {$element: true});
+
+	// Multiple leading underscores
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({__foo_bar: 'value'}), {__fooBar: 'value'});
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({___foo_bar: 'value'}), {___fooBar: 'value'});
+
+	// Multiple leading dollar signs
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({$$foo_bar: 'value'}), {$$fooBar: 'value'});
+
+	// Mixed leading characters
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({$_foo_bar: 'value'}), {$_fooBar: 'value'});
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({_$foo_bar: 'value'}), {_$fooBar: 'value'});
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({__$foo_bar: 'value'}), {__$fooBar: 'value'});
+
+	// With pascalCase option
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({_foo_bar: true}, {pascalCase: true}), {_FooBar: true});
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({$foo_bar: true}, {pascalCase: true}), {$FooBar: true});
+
+	// With deep option
+	t.deepEqual(
+		// eslint-disable-next-line camelcase
+		camelcaseKeys({_outer_key: {$inner_key: 'value'}}, {deep: true}),
+		{_outerKey: {$innerKey: 'value'}},
+	);
+
+	// In arrays
+	t.deepEqual(
+		// eslint-disable-next-line camelcase
+		camelcaseKeys([{_foo_bar: true}, {$bar_foo: false}]),
+		[{_fooBar: true}, {$barFoo: false}],
+	);
+
+	// With preserveConsecutiveUppercase option
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({_foo_BAR: true}, {preserveConsecutiveUppercase: true}), {_fooBAR: true});
+	// eslint-disable-next-line camelcase
+	t.deepEqual(camelcaseKeys({$foo_BAR: true}, {preserveConsecutiveUppercase: true}), {$fooBAR: true});
+});
+
 /**
 Executes the library with the given arguments and resolves with the parsed result.