How to fix a value in a textbox?

Question

I have a textbox to save the user facebook's url.

<tr>
    <td>
        Facebook:
    </td>
    <td>
        <input style="width:300px" type="text" name="facebook" value="http://www.facebook.com/$facebook">
    </td>
</tr>

How can i make the value "http://www.facebook.com/" fixed and uneditable?

UPDATE:

the $facebook part needs to be editable!!

Answer 1

A very simple way is to use the readonly attribute in the "input" HTML tag.

disabled is another property that can be usable.

References: https://www.w3schools.com/tags/tag_input.asp