<script> function foo(){ foo.abc =function(){alert('def')} this.abc =function(){alert('xyz')} abc =function(){alert('@@@@@')}; var abc =function(){alert('$$$$$$')} } foo.prototype.abc =function(){alert('456');} foo.abc =function(){alert('123');} var f =new foo(); f.abc(); // output "xyz" foo.abc(); // output "def" abc(); // if commend " var abc = function(){alert('$$$$$$')} " then you can get "@@@@@" </script>