Form textfield on-click remove default values
What do you mean for "default value"? Do you need to save this value or just to use it as a placeholder?

In this case you can obtain the goal without javascript:

$form['Package']['FirstName'] = array(
  '#type' =&gt; 'textfield',
  '#maxlength'=&gt; 255,
  '#required' =&gt; TRUE,
  '#attributes' =&gt; array(
    'placeholder' =&gt; t('First Name'),
  ),   
);