Support private property identifier in JS lexer (#2076)

lib/rouge/lexers/javascript.rb

@@ -190,8 +190,8 @@ def self.id_regex
 
         rule %r/function(?=(\(.*\)))/, Keyword::Declaration # For anonymous functions
 
-        rule %r/(#{id})[ \t]*(?=(\(.*\)))/m do |m|
-          if self.class.keywords.include? m[1]
+        rule %r/(#?#{id})[ \t]*(?=(\(.*\)))/m do |m|
+          if self.class.keywords.include?(m[1])
             # "if" in "if (...)" or "switch" in "switch (...)" are recognized as keywords.
             token Keyword
           else
@@ -201,7 +201,7 @@ def self.id_regex
 
         rule %r/[{}]/, Punctuation, :statement
 
-        rule id do |m|
+        rule %r/#?#{id}/ do |m|
           if self.class.keywords.include? m[0]
             token Keyword
             push :expr_start

spec/visual/samples/javascript

@@ -297,3 +297,21 @@ ret += "\n";
 
 let baz;
 baz ??= 'default';
+
+class ClassWithPrivate {
+  #privateField;
+  #privateFieldWithInitializer = 42;
+
+  #privateMethod(obj) {
+    if (#privateField in obj) return obj.#privateField;
+
+    return "invalid obj"
+  }
+
+  static #privateStaticField;
+  static #privateStaticFieldWithInitializer = 42;
+
+  static #privateStaticMethod() {
+    // …
+  }
+}