JavaScript auto filling credentials

Okay so I've been working on a steam account generator for a day or two now but I've been suck on one thing and it's, when I change the value of the password the steam webpage doesn't detect it. (as shown in picture 1) I've looked in a lot of places and can't seem to find a fix :/ any suggestions? I'm stuck and don't really know how to get around this... You can see that everything gets filled in find but the website doesn't recongize characters are in the password box

Picture 1

document.getElementById('password').value = 'erertert';
CheckPasswordStrength();
document.getElementById('reenter_password').value = 'erertert';
ReenterPasswordChange();

Seems to work.