Is it possible to upload a text file to input in HTML/JS?

Question

I have some input boxes in a HTML form that need to be updated when the form loads and these values need to be uploaded from a text file.
A similar question was also asked h

Answer 1

The other answer is great, but a bit outdated and it requires HTML & jQuery to run.

Here is how I do it, works in all modern browsers down to IE11.

/**
 * Creates a file upload dialog and returns text in promise
 * @returns {Promise}
 */
function uploadText() {
    return new Promise((resolve) => {
        // create file input
        const uploader = document.createElement('input')
        uploader.type = 'file'
        uploader.style.display = 'none'

        // listen for files
        uploader.addEventListener('change', () => {
            const files = uploader.files

            if (files.length) {
                const reader = new FileReader()
                reader.addEventListener('load', () => {
                    uploader.parentNode.removeChild(uploader)
                    resolve(reader.result)
                })
                reader.readAsText(files[0])
            }
        })

        // trigger input
        document.body.appendChild(uploader)
        uploader.click()
    })
}

// usage example
uploadText().then(text => {
     console.log(text)
})
// async usage example
const text = await uploadText()