Placing Javascript function arguments into objects

[gamerman0203]

Ok, so here is what I want to do. I want to take the argument "1" and place it into the form reference object like this.

function calc( i){
document.form.quantity i.value
}
...
...
<input type="text" onFocus="calc( 1)">

This is what I've tried:

document.form.quantity[i].value
var quantity = 'document.form.quantity' + i + '.value'
document.form[quantity[i]].value
document.form.quantity+i.value
document.form.[quantity[i]].value

I realize some of those aren't proper sytax, but I was getting desperate.

The only thing that gets atleast halfway is the second example, but that just makes is a string. I need it to retain it's object functionality.

Any ideas?

Or if you know how I can turn a string back into an object, that would work also.

Many thanks in advance.