Setting the id attribute with knockoutjs including a prefix

I'm using KnockoutJS to iterate over an object, like this: Now this all works. But the problem i have is that it sets the `id` of the `button` to just a number. So it looks like this: ``` <button id="1">Button 1</button> <button id="3">Button 2</button> <button id="8">Button 3</button> ``` So i tried to put a prefix in front of the the 'Id' property, like so: ``` <div data-bind="foreach:Items"> <button data-bind="text: Name, attr: {'id': 'myprefix_' + Id}"></button> </div> ``` But that doesn't seem to be working. My `id` gets filled with some Knockout observable function when i do it like that... So my question is, how can i add a prefix when i specify the `id` attribute of a field?