这将产生相同的结果：

var select = document.querySelector("select"),
    button = document.querySelector("button");

select.addEventListener("change", function(e) {
    var option = this.options[this.selectedIndex];

    switch (option.id) {
        case "zero": button.value = "Choose Location"; break;
        case "one": button.value = "Location one"; break;
        case "two": button.value = "Location two"; break;
        case "three": button.value = "Location three"; break;
    }
});

小提琴