iD/modules/util/get_set_value.js

// Like selection.property('value', ...), but avoids no-op value sets,
// which can result in layout/repaint thrashing in some situations.
export function getSetValue(target, value) {
    function d3_selection_value(value) {
        function valueNull() {
            delete target.value;
        }

        function valueConstant() {
            if (target.value !== value) {
                target.value = value;
            }
        }

        function valueFunction() {
            var x = value.apply(target, arguments);
            if (x == null) {
                delete target.value;
            }
            else if (target.value !== x) {
                target.value = x;
            }
        }

        return value == null
            ? valueNull : (typeof value === 'function'
            ? valueFunction : valueConstant);
    }

    if (!arguments.length) {
        return target.property('value');
    }
    return target.each(d3_selection_value(value));
}