How to limit the maximum files chosen using JavaScript

We use the multiple attribute on the HTML <input type="file"> element to allow multiple file uploads in our HTML forms.

However, the <input> element does not provide any attribute to specify how many files can be uploaded at once.

For limiting the maximum number of files chosen for upload, we have to use JavaScript.

Let us say you have the following HTML element for files upload:

<input type="file" id="avatars" multiple>

Now you want to make sure that only 2 files are uploaded at once. Here is how you can do it:

const input = document.querySelector('#avatars');

// Listen for files selection
input.addEventListener('change', (e) => {
    // Retrieve all files
    const files = input.files;

    // Check files count
    if (files.length > 2) {
        alert(`Only 2 files are allowed to upload.`);
        return;
    }

    // TODO: continue uploading on server
});

The input.files property return a FileList object. We then check the number of elements in FileList to make sure they do not exceed the maximum allowed limit.

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