如何限制使用多个文件输入时选择的最大文件数

You could run some jQuery client-side validation to check:

$(function(){
$("input[type='submit']").click(function(){
var $fileUpload = $("input[type='file']");
if (parseInt($fileUpload.get(0).files.length)>2){
alert("You can only upload a maximum of 2 files");
}
});
});​

http://jsfiddle.net/Curt/u4NuH/

But remember to check on the server side too as client-side validation can be bypassed quite easily.

Use two <input type=file> elements instead, without the multiple attribute.

You should also consider using libraries to do that: they allow limiting and much more:

• FineUploader. Demo using validation.itemLimit as of 5.16.2:

  var restrictedUploader = new qq.FineUploader({
  validation: {
  itemLimit: 3,
  }
  });
  

• bluimp's jQuery File Upload Plugin. Usage: jquery file upload restricting number of files using maxNumberOfFiles as of v9.22.0:

  $('#fileuploadbasic').fileupload({
  maxNumberOfFiles: 6
  });
  

They are also available at https://cdnjs.com/

On change of the input track how many files are selected:

$("#image").on("change", function() {
if ($("#image")[0].files.length > 2) {
alert("You can select only 2 images");
} else {
$("#imageUploadForm").submit();
}
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<strong>On change of the input track how many files are selected:</strong>
<input name="image[]" id="image" type="file"  multiple="multiple" accept="image/jpg, image/jpeg" >

This should work and protect your form from being submitted if the number of files is greater then max_file_number.

$(function() {


var // Define maximum number of files.
max_file_number = 3,
// Define your form id or class or just tag.
$form = $('form'),
// Define your upload field class or id or tag.
$file_upload = $('#image_upload', $form),
// Define your submit class or id or tag.
$button = $('.submit', $form);


// Disable submit button on page ready.
$button.prop('disabled', 'disabled');


$file_upload.on('change', function () {
var number_of_images = $(this)[0].files.length;
if (number_of_images > max_file_number) {
alert(`You can upload maximum ${max_file_number} files.`);
$(this).val('');
$button.prop('disabled', 'disabled');
} else {
$button.prop('disabled', false);
}
});
});

if you want php you can count the array and just make an if statement like

if((int)count($_FILES['i_dont_know_whats_coming_next'] > 2)
echo "error message";

Another possible solution with JS

function onSelect(e) {
if (e.files.length > 5) {
alert("Only 5 files accepted.");
e.preventDefault();
}
}

In javascript you can do something like this

<input
ref="fileInput"
multiple
type="file"
style="display: none"
@change="trySubmitFile"
>

and the function can be something like this.

trySubmitFile(e) {
if (this.disabled) return;
const files = e.target.files || e.dataTransfer.files;
if (files.length > 5) {
alert('You are only allowed to upload a maximum of 2 files at a time');
}
if (!files.length) return;
for (let i = 0; i < Math.min(files.length, 2); i++) {
this.fileCallback(files[i]);
}
}

I am also searching for a solution where this can be limited at the time of selecting files but until now I could not find anything like that.