js时间加减

 选中时间间隔，选择一个日期，另一个日期自动确定。

js中String类型转成date格式

var date = new Date("2020-1-6 14:58:43");

核心代码

var date = new Date(选中的时间);

 date.setDate(date.getDate()+n);

<div class="col-lg-4 col-md-4 col-xs-4 col-sm-4" style="width: 30rem;">
                        &emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&ensp;<input class="beginDate" name="tradeStartTime" type="text" onchange="checkDate()" readonly="readonly" id="tradeStartTime" style="width: 100px;">
                        <span>--</span>
                        <input class="beginDate" type="text" readonly="readonly" id="tradeEndTime"  onchange="checkEndDate()" name="tradeEndTime" style="width: 100px;margin-right: 10px">
                        <button type="button" class="btn btn-info" style="margin-right: 10px;margin-bottom: 3px" onclick="findPt()">
                            确定
                        </button>
                    </div>

function checkDate() {
        var tradeStartTime = $("#tradeStartTime").val();
        var tradeEndTime = $("#tradeEndTime").val();
        var interval = $("input[name=interval]:checked").val();
        var date = new Date(tradeStartTime);
        switch (interval) {
            case "TOD":
                date = date.getFullYear() + '-' + (date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1) + '-' + (date.getDate()  < 10 ? "0" + (date.getDate()) : date.getDate());
                $("#tradeEndTime").val(date);
                break;
            case "1W":
                date.setDate(date.getDate()+7);
                date = date.getFullYear() + '-' + (date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1) + '-' + (date.getDate() < 10 ? "0" + (date.getDate()) : date.getDate());
                $("#tradeEndTime").val(date);
                break;
            case "2W":
                date.setDate(date.getDate()+14);
                date = date.getFullYear() + '-' + (date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1) + '-' + (date.getDate() < 10 ? "0" + (date.getDate()) : date.getDate());
                $("#tradeEndTime").val(date);
                break;
            case "1M":
                date.setMonth(date.getMonth()+1);
                date = date.getFullYear() + '-' + (date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1) + '-' + (date.getDate() < 10 ? "0" + (date.getDate()) : date.getDate());
                $("#tradeEndTime").val(date);
                break;
            case "3M":
                date.setMonth(date.getMonth()+3);
                date = date.getFullYear() + '-' + (date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1) + '-' + (date.getDate() < 10 ? "0" + (date.getDate()) : date.getDate());
                $("#tradeEndTime").val(date);
                break;
            case "6M":
                date.setMonth(date.getMonth()+6);
                date = date.getFullYear() + '-' + (date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1) + '-' + (date.getDate() < 10 ? "0" + (date.getDate()) : date.getDate());
                $("#tradeEndTime").val(date);
                break;
            case "1T":
                date.setFullYear(date.getFullYear()+1);
                date = date.getFullYear() + '-' + (date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1) + '-' + (date.getDate() < 10 ? "0" + (date.getDate()) : date.getDate());
                $("#tradeEndTime").val(date);
                break;
            default:
                date = date.getFullYear() + '-' + (date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1) + '-' + (date.getDate()  < 10 ? "0" + (date.getDate() ) : date.getDate() );
                $("#tradeEndTime").val(date);
                break;
        }

    }