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 here: Uploading Text File to Input in Html/JS

I have searched for this on the internet, but couldn't find any correct answer. So I want to know whether it is possible or not?

Answer 1

If you wish to go the client side route, you'll be interested in the HTML5 FileReader API. Unfortunately, there is not wide browser support for this, so you may want to consider who will be using the functionality. Works in latest Chrome and Firefox, I think.

Here's a practical example: http://www.html5rocks.com/en/tutorials/file/dndfiles/#toc-reading-files

And I also read here to find the readAsText method: http://www.w3.org/TR/file-upload/#dfn-readAsText

I would do something like this (jQuery for brevity): http://jsfiddle.net/AjaDT/2/

Javascript

var fileInput = $('#files');
var uploadButton = $('#upload');

uploadButton.on('click', function() {
    if (!window.FileReader) {
        alert('Your browser is not supported');
        return false;
    }
    var input = fileInput.get(0);

    // Create a reader object
    var reader = new FileReader();
    if (input.files.length) {
        var textFile = input.files[0];
        // Read the file
        reader.readAsText(textFile);
        // When it's loaded, process it
        $(reader).on('load', processFile);
    } else {
        alert('Please upload a file before continuing')
    } 
});

function processFile(e) {
    var file = e.target.result,
        results;
    if (file && file.length) {
        results = file.split("\n");
        $('#name').val(results[0]);
        $('#age').val(results[1]);
    }
}

Text file

Jon
25

Answer 2

The other answer is great, but a bit outdated and it requires HTML & jQuery to run.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<any>}
 */
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()