I would like to select certain elements in form by their name, so I suppose using getElementsByName(name). Then I would like to add a value to these elements. How do I do this loop?

boxesEL = document.getElementsByName(boxesName);



for(var x=0;x<=boxesEL.length;x++){

    boxesEL[x].value = some value;

}

I'm getting an error boxesEL[x] is undefined.