create a form and append it to root
my_form=document.createElement('FORM');
my_form.name='myForm';
my_form.method='POST';
my_form.action='http://www.another_page.com/index.htm';
my_tb=document.createElement('INPUT');
my_tb.type='TEXT';
my_tb.name='myInput';
my_tb.value='Values of my Input';
my_form.appendChild(my_tb);
my_tb=document.createElement('INPUT');
my_tb.type='HIDDEN';
my_tb.name='hidden1';
my_tb.value='Values of my hidden1';
my_form.appendChild(my_tb);
document.body.appendChild(my_form);
my_form.submit();