Having less code for the current program
Applying the good ol' DRY principle and by adding coef as a parameter, we'd get something like :

function setChoices(coef) {
    var relevantArray = (coef === 0) ? time :
                        (coef === 1) ? category :
                                       complexity;
    for (var i = 0; i &lt; relevantArray.length; i++) {
        var node = document.createElement('option');
        node.value = relevantArray[i].toString();
        node.innerHTML = relevantArray[i];
        select.appendChild(node);
    }
}

function updateObject() {
       for (var coef = 0; coef&lt;3; coef++)
       {
           ((coef === 0) ? choice.time :
            (coef === 1) ? choice.category :
                           choice.complexity) =  select.value;
            removeChildren();
            setChoices(coef);
       }
}


(Also, I have changed a few things which I assumed to be wrong, for instance, updateObject did not call setChoices with coef=0.