HTML检测输入已完成自动填写下一个内容的实现方

<tbody>
    <tr style="background-color:#FfFFFF">
        <th colspan="2" class="info">出差补贴:</th>
    </tr>
    <tr style="background-color:#F3F3F3">
        <th>补贴天数:</th>
        <td>
            <input class="form-control" onBlur="finnishInput(event)" "onInput(event)" id="travelAllowanceDaysId" type="number" placeholder="">
        </td>
    </tr>
    <tr style="background-color:#FFFFFF">
        <th>补贴金额:</th>
        <td>
            <input class="form-control" id="travelAllowanceFeesId" type="number" placeholder="">
        </td>
    </tr>
</tbody>

var flag = 0;

function onInput(e) {
    console.log("Inputing");
    flag = 1;
    $api.removeAttr($api.byId('travelAllowanceFeesId'), 'readonly');
}

function finnishInput(e) {
    if (1 == flag) {
        console.log("InputOk");
        flag = 0;

        $api.byId('travelAllowanceFeesId').value = 400$api.byId('travelAllowanceDaysId').value;
        $api.attr($api.byId('travelAllowanceFeesId'), 'readonly', true);
    }
}