How To Make A Textbox Readonly Based On Its Value

Is there anyway that we can make a textbox readonly based on the value it has.

I mean,

If we have

<INPUT class="ms-input" ID=onetidIOViewName
value="AllItems" name="NewViewFileName"
size="20" title="File name">

since it has"AllItems", it the textbox should become readonly.

but the text box should be editable if

<INPUT class="ms-input" ID=onetidIOViewName
value="xyzxyz" name="NewViewFileName"
size="20" title="File name">

I am trying it like this,


var check = document.getElementById("onetidIOViewName").value;
if(check == 'AllItems')
{
document.getElementById("onetidIOViewName").innerHTML += 'ReadOnly>' ;
}