javascript regular expression check for the right file type

On 07.26.12, In 116, javascript, by sc_7cabc029490e9fcb99b8d58793c625bd
javascript regular expression check for the right file type
var image = 'test.doc';

var valid_extensions = /(.jpg|.jpeg|.gif)$/i;   


if(valid_extensions.test(image)){ 
   alert('OK');
}else{
   alert('Invalid File')
}