<select onchange="changeBottomTimeScale(this.value)" style="margin-right : 20px;">
    <option value="year">年 </option>
    <option value="halfyear">半年 </option>
    <option value="quarter">季度 </option>
    <option value="month">月 </option>
    <option value="week">周 </option>
    <option value="day" selected>日 </option>
    <option value="hour">时 </option>
</select >

function changeBottomTimeScale(value) {
    gantt.setBottomTimeScale(value)
}