amis中月份选择组件，如何设定值为月末最后一天

需求：选择月份，表单提交时，提交的值是月末最后一天

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    "body": [
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        "id": "u:b156da001a16",
        "type": "form",
        "title": "表单",
        "mode": "horizontal",
        "dsType": "api",
        "feat": "Insert",
        "body": [
          {
            "type": "input-month",
            "label": "日期",
            "name": "mydate",
            "id": "u:dcb628073830",
            "placeholder": "请选择月份",
            "valueFormat": "YYYY-MM-DD",
            "displayFormat": "YYYY-MM",
            "minDate": "",
            "maxDate": "",
            "value": "",
            "onEvent": {
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                "actions": [
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                    "ignoreError": false,
                    "script": "setTimeout(function () {\n  let date = new Date( context.props.formStore.data.mydate);\n  let year = date.getFullYear();\n  let month = date.getMonth() + 1;\n  let l = new Date(year, month, 0).getDate();\n  let lastday = year +\"-\"+ month+\"-\" + l;\n\n  context.props.formStore.setValues({ lastday: lastday });\n\n  console.log(context.props.data.mydate);\n},500)\n\n",
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            "autoFill": {
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          {
            "type": "input-text",
            "label": "月末",
            "name": "lastday",
            "id": "u:53abff2c83bb",
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