Merge remote files using JavaScript

Use something like this to download the contents of each file, load them into an array, then act on the array when all the files are done downloading. It wil require s ome more logic to assemble the files and to make sure all the files are actually done downloading, but it is possible.

function dl(target, callback) {

    var xhr = new XMLHttpRequest();
    xhr.onreadystatechange = function() {
        if (xhr.readyState == XMLHttpRequest.DONE) {
            callback(xhr.responseText);
        }
    }
    xhr.open("GET", target, true);
    xhr.send();
}

dl("file_a", onDone);
dl("file_b", onDone);

document.files = new Array();
function onDone(data) {

    document.files.push(data);
}

Then use something like this to download the files from the JS cache to the users desktop.

function download() {

    var hiddenElement = document.createElement('a');

    hiddenElement.href = 'data:attachment/text,' + encodeURI(document.files);
    hiddenElement.target = '_blank';
    hiddenElement.download = 'in-line.txt';
    hiddenElement.click();
}