//1.prop中是第一個要驗證的值
<el-form-item label="期望薪資" prop="lowSalary">
    <el-select v-model="jobExpectations.lowSalary" placeholder="請選擇" class="thirty-seven-percent">
        <el-option
                value="999K">
        </el-option>
    </el-select>
    至
    <el-select v-model="jobExpectations.heightSalary" placeholder="請選擇" class="thirty-seven-percent">
        <el-option
                value="9999K">
        </el-option>
    </el-select>
</el-form-item>
//2.在驗證規則中新增validator驗證規則

lowSalary: [
    {required: true, validator:customDefinition, message: '請選擇薪資', trigger: 'change'},
],

//3.在data中定義customDefinition的判斷條件

data() {
    const customDefinition = (rule,value,callback)=>{

        if(value===""||value===null) {
            callback(new Error('請選擇日期'))
        }else if(this.jobExpectations.heightSalary===""||this.jobExpectations.heightSalary===null){
            callback(new Error())
        }else{
            callback()
        }
    }
    return {}
}