Develop Reference

How can I remove specific images from a file input?

I am creating a product registration using php and using vanilla js to get the selected images from the file input and preview them in the screen. Now I want to provide a way for the user to remove unwanted images before submitting the form.
The form has the images and other inputs for the title of the product, description, price and category selection.
I have seen so far in many places people telling that you can use a dataTransfer object to store the images and remove from the dataTransfer and after making the file input (=) the dataTransfer but none of the answers I've found so far have worked.
Is there a way to remove images from the file input once they are selected?

#CBroe I'm talking about Data Transfer in js (https://developer.mozilla.org/en-US/docs/Web/API/DataTransfer). Thank you for your comment. If it's not possible to remove files from the filelist of the file input I will have to store those data somewhere and create an arbitrary submission of the form.
Thank you

#RiggsFolly the user clicks on the file input <input type="file" multiple> and selects (let's say) 4 images. These images are read by the js script and displayed on the screen, as a preview. I want to provide a small garbage icon on top of each image and let the user be able to remove specific images.
I wanted to know if it's possible to remove the selected images from the files inserted on the file input. Then I would remove the image using the name of the file as reference (or any other reference). I just never found a way to remove files from the input file.

Dropzone with draggable area and input in different locations

I'm trying to use Dropzone in my application to enable drag and drop upload. The problem is: I can't upload the file at the time I select a file, I need to wait the user click on 'Submit' on entire form (I don't have a form only to file upload) to upload my file.
And I have another problem, the draggable area (my div) is not in the same place as my input (where I need my uploaded file).
It's something like this:
<form ...>
<input type="file"/>
</form>
<div id="myDivWhereUserWillDropTheFile">
</div>
Is that possible to solve with Dropzone?

It depends on the exact flow you want to achieve, but to disable autoupload take a took at autoProcessQueue and autoQueue options.
http://www.dropzonejs.com/#config-autoProcessQueue
From there you can use a addedfile event handler to programmatically set your input
http://www.dropzonejs.com/#event-addedfile

Only one file is uploaded when choosing multiple files in input type

User click the uploader several times to upload multiple files(for example, a.txt, b.txt, c.txt), but server can only receive the last file(c.txt). Is there anything else needed to implement multiple files uploader?
<form action="storeArticle" method="post" enctype="multipart/form-data">
<input type="file" name="file[]" multiple >
<input type="submit" name="submit" class="submit" id="submit" value="submit" />
</form>
==========
What I want to implement is like https://stackoverflow.com/questions/ask. User can click the image icon as many times as they want, and finally all the images will be sent to server conrrectly.

When you say they click the uploader several times, do you mean having to open the file explorer each time to add one file? If so, then this will cause it to lose the other files that were previously selected.
The way to fix this is for your users to ctrl/cmd+click each file they want while only opening the file explorer once.
File inputs even remove the selected file when you open a file explorer and then press cancel.
EDIT
Just a thought, I'm on a phone so I can't test this but maybe you can play around with it...
have an input field that will be there from start to finish. When they select their first file, make the button (best to use a <label>) they click no longer open that file input. Instead, append a dynamic file input and make the label's for attribute equal to the dynamically added file input. After you add the dynamic input, create a listener for it so when the user selects a file in that new input it is appended to the original input.files array. Once this happens the process starts all over again, the dynamic input handles the file selection and passes it to the original input when a file is selected.
The reason it is best to hide the actual choose file button is because it can be a bit inconsistent at times. Instead, using the label element with the input element's id as the label's for attribute guarantees that clicking the label will focus the file upload field.

I was going to add this as a comment, but I can't.
Have you tried cloning the input and adding it to the form?
Then when the user selects a file you would could either add the new input, add the new input and hide the "populated" ones, or add the new input and mark the "populated" ones as readonly (you would want to add some method to remove them).

HTML5 File Upload Input - onChange

When the user selects files to be uploaded I present one of two buttons to take action on the file(s) based on how many files there are. I get the number of files by including an onchange=getNumFiles(this) in the file input tag.
My problem is that I hide the button to take action on the files after the user clicks it, and if the user selects the same file(s) a second time the button is not "re-presented". This is happening because the file upload input never actually changed because the input is still holding the original file selection. How can I account for this?
Is there a way to clear the contents of the file upload input? I've tried setting the value to null to no avail. Or is there a different event other than onchange that I should be using? hope this makes sense....

"Is there a way to clear the contents of the file upload input"
Yes, call .reset() on the form.
$("#myform")[0].reset();
Now if the same file is selected again it will correctly trigger a change event since it changed from nothing to something again.

Multiple input how to keep old values when reselecting files

I have simple multiple selection input
<input multiple="true" type="file" name="image_name[]" />
Now i would like to keep selecting files with this one input and then submit my form
what i mean after selecting some files if i try to do it once more my old selection is removed, is there some kind of way to keep adding selections to that input?
If not what else could i do? I'm thinking of creating new input and hiding old one and so after user finishes selecting everything, just submit all inputs at once, would that be the right way to do it?

The multiple attribute in <input type=file> is a new feature in HTML5 with limited browser support. Are you using html5 doctype? If so try with multiple="multiple" instead, or just multiple.
In any way, I suggest you use something like plupload for this.
EDIT:
To select multiple files you need to Shift+Select them.