我只是想把用户的图像上传的形式与识别号码。问题是，如果用户在没有填写任何内容的情况下按下submit，它会根据脚本显示一个警告，但随后会重定向到提供的POST链接。它不应该是这样的，我想阻止POST操作，如果有任何验证问题。我也没有看到这个片段的任何错误/日志错误。
这是我的代码-

<div class="row">
    <div class="col-12 col-md-12 col-sm-6">
        <!-- Attendacne Card Info Fields-->
        <div class="card">
            <div class="card-body">
                <!--<h4 class="card-title mb-5">DSR Information Fields</h4>-->
                <form action="./collect-dsrs-attendance-confirmation.php" method="POST" name="page331" enctype="multipart/form-data" onsubmit="return validate();">
                    <div class="form-body">
                        <div class="row">
                            <input type="text" class="form-control"  id="lat" name="latitude" style="display:none;" value="">
                            <input type="text" class="form-control"  id="long" name="longitude" style="display:none;" value="">
                            <!--Back Button For Each Page-->
                            <div class="col-md-12 mb-5 d-grid gap-2 d-md-flex justify-content-md-end">
                                <div class="form-actions text-start mt-3">
                                    <a type="button" href="./index.php" class="btn btn-danger ps-4 pe-4"
                                    id="backhome" style="background-color: rgb(255, 0, 0);">Back Home</a>
                                </div>
                            </div>   
    
                            <div class="col-lg-12 col-md-12">
                                <div class="form-group mb-3">
                                        <label class="form-label text-dark" for="dsrELNumber">ইএল নম্বর</label>
                                        <div class="input-group">
                                            <div class="input-group-prepend">
                                                <span class="input-group-text" id="basic-addon1">+880</span>
                                            </div>
                                            <input class="form-control" id="dsrELNumber" type="text" name="el_number" id="elNumber" 
                                            placeholder="Enter EL Number"  data-maxlength="10" data-minlength="10"
                                            oninput="this.value=this.value.slice(0,this.dataset.maxlength)"
                                            value="<?php if(!empty($_POST['dsr_el_number'])) echo $_POST['el_number']; ?>" required>
                                        </div>
                                        <div id="docImage">
                                            <!--<video id="video" width="640" height="480" autoplay style="display:none;"></video>-->
                                            <label class="custom-file-label text-primary mt-3" for="file-input">Take Selfie</label>
                                            <input type="file" class="mt-4 form-control" id="captureDocument" name="user_img" accept="image/*" capture="camera" required>
                                            <button class="btn text-white mt-4 mb-4 d-block ps-4 pe-4" type="submit" style="background-color: rgb(255, 0, 0);" id="btnTakeDocument">Submit</button>
                                        </div>
                                
                                     <!--To show successfull message-->
                                     <div id="message"></div>
                                </div>
                            </div>
                        </div>
                    </div>
                </form>
            </div>
        </div>
        <!-- Attendacne Card Info Fields-->
    </div>
</div>
<script>
    function validate()
    {
        var valid = true;
        var file_name = "";
        var file_type = "";
        var file_size = "";
        var error_msg = "";
        var valid_size = 3*1000*1000;
        var display_error = document.getElementById('file_error');
        var file = document.getElementById("user_img");
     
        if(file.files.length != 0)
        {
            file_name = file.files[0].name;
            file_size = file.files[0].size;
            file_type = file.files[0].type;
             
            if(file_type!="image/png" && file_type!="image/jpeg" && file_type!="image/gif")
            {
                valid = false;
                error_msg = error_msg + "\n* Only 'PNG', 'JPG/JPEG' and 'GIF' file type supported.";
            }
     
            if(file_size > valid_size)
            {
                valid = false;
                error_msg = error_msg + "\n* Filesize should be upto 3MB.";
            }
     
        }
        else
        {
            valid = false;
            error_msg = error_msg + "\n* Please select any image file.";
        }
     
     
        if(valid==true)
        {
            alert("File pass all validation. Now it is ready to send.");
            /*Write ajax code here to send file to the server.*/
            return true;
        }
        else
        {
            display_error.innerHTML = error_msg;
            return false;
        }
     return valid; 
    }
</script>