Javascript utilities

/*
 * is_number
 *  Return true if a value represents a number, else return false.
 */
function is_number(value)
{
    var str = value + "";
    return str.match(/^-?\d*\.?\d+$/) ? true : false;
}
/*
 * is_blank
 *  Return true if value is a blank (i.e. "").
 */
function is_blank(value)
{
    var str = value + "";
    return str.match(/^\s*$/) ? true : false;
}


/*
 * trim_string
 *  Remove leading and trailing blank spaces from a string.
 */
function trim_string(str)
{
    var trim = str + "";
    trim = trim.replace(/^\s*/, "");
    return trim.replace(/\s*$/, "");
}
/*
 * are_values_equal()
 *  Compare values of types boolean, string and number. The types may be different.
 *  Returns true if values are equal.
 */
function are_values_equal(val1, val2)
{
    /* Make sure we can handle these values. */
    switch (typeof(val1)) {
    case 'boolean':
    case 'string':
    case 'number':
        break;
    default:
        // alert("are_values_equal does not handle the type '" + typeof(val1) + "' of val1 '" + val1 + "'.");
        return false;
    }

    switch (typeof(val2)) {
    case 'boolean':
        switch (typeof(val1)) {
        case 'boolean':
            return (val1 == val2);
        case 'string':
            if (val2) {
                return (val1 == "1" || val1.toLowerCase() == "true" || val1.toLowerCase() == "on");
            } else {
                return (val1 == "0" || val1.toLowerCase() == "false" || val1.toLowerCase() == "off");
            }
            break;
        case 'number':
            return (val1 == val2 * 1);
        }
        break;
    case 'string':
        switch (typeof(val1)) {
        case 'boolean':
            if (val1) {
                return (val2 == "1" || val2.toLowerCase() == "true" || val2.toLowerCase() == "on");
            } else {
                return (val2 == "0" || val2.toLowerCase() == "false" || val2.toLowerCase() == "off");
            }
            break;
        case 'string':
            if (val2 == "1" || val2.toLowerCase() == "true" || val2.toLowerCase() == "on") {
                return (val1 == "1" || val1.toLowerCase() == "true" || val1.toLowerCase() == "on");
            }
            if (val2 == "0" || val2.toLowerCase() == "false" || val2.toLowerCase() == "off") {
                return (val1 == "0" || val1.toLowerCase() == "false" || val1.toLowerCase() == "off");
            }
            return (val2 == val1);
        case 'number':
            if (val2 == "1" || val2.toLowerCase() == "true" || val2.toLowerCase() == "on") {
                return (val1 == 1);
            }
            if (val2 == "0" || val2.toLowerCase() == "false" || val2.toLowerCase() == "off") {
                return (val1 === 0);
            }
            return (val2 == val1 + "");
        }
        break;
    case 'number':
        switch (typeof(val1)) {
        case 'boolean':
            return (val1 * 1 == val2);
        case 'string':
            if (val1 == "1" || val1.toLowerCase() == "true" || val1.toLowerCase() == "on") {
                return (val2 == 1);
            }
            if (val1 == "0" || val1.toLowerCase() == "false" || val1.toLowerCase() == "off") {
                return (val2 === 0);
            }
            return (val1 == val2 + "");
        case 'number':
            return (val2 == val1);
        }
        break;
    default:
        return false;
    }
}
/*
 * copy_select_options(from_select, to_select )
 *  copy options from the given select element. Do not copy the first option which is the descriptive
 *      label such as <option value="-1">Computer Name</option>
 *
 * NOTE: Attempts to preserve the current selection, or reverts to "-1" if the selection has disappeared.
 */
function copy_select_options(from_select, to_select)
{
        /*
         * Disable the select element so that it does not conflict with any user-interaction
         */
        var saved_state = to_select.disabled;

        if (!saved_state) {
            to_select.disabled = true;
        }

        /*
         * Remember the selection value of this pulldown, if any
         */
        var current_value_selection = null;
        if (to_select.selectedIndex) {
            var current_selected_index = to_select.selectedIndex;
            current_value_selection = to_select.value;
        } else {
            current_value_selection = "-1";
        }

        /*
         * Clear the select options as we are now going to refresh the list
         *  Keep the descriptive label
         */
        for (var k = to_select.options.length - 1; k > 0; k--) {
            to_select.options[k] = null;
        }

        /*
         * Copy options from the new select
         *  Don't touch the descriptive label, start from entry 1
         *  opt.text = "Computer Name"; opt.value = "-1";
         */
        var selected_index = 0;
        for (var entry = 1; entry < from_select.options.length; ++entry) {
            to_select.options.add(new Option(from_select.options[entry].text, from_select.options[entry].value));

            /*
             * If the previously selected value matches this entry then we remeber the
             * index of it so that we can restore the selected position
             */
            if (from_select.options[entry].value == current_value_selection) {
                selected_index = entry;
            }
        }

        /*
         * Restore the selected position
         */
        to_select.selectedIndex = selected_index;

        /*
         * Re-enable the select element
         */
        to_select.disabled = saved_state;
}