Running JavaScript downloaded with XMLHttpRequest

I have a site that loads information using the XMLHttpRequest when a user clicks a link. The system works well but I would like to be able to execute JavaScript gathered in this 开发者_C百科process.

This is a problem as I would like to download the scripts 'on demand' if it were, rather than loading them all when the page is loaded.

Thanks for any help

I believe the recommended solution is something like this:

function include(scriptUrl)
{
    var xmlhttp = new XMLHttpRequest();
    xmlhttp.open("GET", scriptUrl);
    xmlhttp.onreadystatechange = function()
    {
        if ((xmlhttp.status == 200) && (xmlhttp.readyState == 4))
        {
            eval(xmlhttp.responseText);
        }
    };
    xmlhttp.send();
}

Or something like it.

However, be wary of this approach. It's vulnerable to cross-site scripting, which can open you (and your users) up to all sorts of nastiness. You'll want to take suitable precautions.

Recently I found the answer (It works in Chrome, in another browsers it was not tested).

You can create dataURL string and put it into src attribute of script element.

var xhr = XMLHttpRequest(),
    doc = document;
xhr.open('GET', pathToJSFile, true);
xhr.onload = function () {

    var script = doc.createElement('script'),
        base64 = 'data:application/javascript;base64,';
    try {
        base64 += btoa(data.responseText);
    } catch (e) {
        // script file may contain characters that not included in Latin1
        var symbols = data.responseText.split('');
        for (var i = 0, l = symbols.length; i < l; i++) {
            var symbol = symbols[i];
            // here we are trying to find these symbols in catch branch
            try {
                btoa(symbol);
            } catch (e) {
                var code = symbol.charCodeAt(0).toString(16);
                while (code.length < 4) {
                    code = '0' + code;
                }
                // replace original symbol to unicode character
                symbols[i] = '\\u' + code;
            }
        }
        // create new base64 string from string with replaced characters
        base64 += btoa(symbols.join(''));
    } finally {
        script.src = base64;
        // run script
        doc.body.appendChild(script);
    }

};
xhr.send();

You can subscribe to xhr.onprogress to show progress bar.

Update. You can download your script file as blob, and then create blob-url.

var xhr = XMLHttpRequest(),
    doc = document;
xhr.responseType = 'blob';
xhr.open('GET', pathToJSFile, true);
xhr.onload = function () {

    var script = doc.createElement('script'),
        src = URL.createObjectURL(xhr.response);

    script.src = src;
    doc.body.appendChild(script);
};
xhr.send();

You can run script downloaded in form of a string using

eval()

However I would recommend you to add new

<script src='..'></script>

to your document and have a callback which will be called when it will be downloaded. There are many utils and jquery plug-ins for that.

I had the challenge on a mobile web-project, the magic was to set "overrideMimeType". This has been verified to work on Android 4.1 to Android 6.0.

var head = document.getElementsByTagName('head');
var injectedScript = document.createElement('script');
head[0].appendChild(injectedScript);

var myRequest = new XMLHttpRequest();
myRequest.onreadystatechange = function() {
  if (myRequest.readyState == 4 && myRequest.status == 200) {
        injectedScript.innerHTML = myRequest.responseText;
    //run a function in the script to load it   
  }
};

function start(){
    myRequest.open('GET', 'javascript-url-to-download', true);
    myRequest.overrideMimeType('application/javascript');
    myRequest.send();
}

start();

You would need to use eval to parse the javascript from the XHR, note that this is EXTREMELY dangerous if you don't have absolute trust in the source of the javascript.