Implementing a Button to Check for Latest Form Version

[Kaxkul]

Hi everyone,
I'm trying to generate a button in my form to allow users to check if they downloaded the latest version online by implementing the code below. For some reason, it doesn't work. I defined the URL of the server where the latest form version is hosted and the latest file name allocated, but it still doesn't run. Any idea why?
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var versionCheckUrl = "https://example.com/checkformversion";var xhr = new XMLHttpRequest();
xhr.open("GET", versionCheckUrl, true);
xhr.onreadystatechange = function() {
if (xhr.readyState == 4 && xhr.status == 200) {
var latestVersion = xhr.responseText;

var currentVersion = this.getField("versionField").value;

if (latestVersion === currentVersion) {
app.alert("You have the latest version of the form.");
} else {
app.alert("A newer version of the form is available. Please download it from our website.");
}
}
};
xhr.send();

[Bernd Alheit]

Check the JavaScript console (ctrl-j) for errors.

[Kaxkul]

Thanks @Bernd Alheit I couldn't figure out the issue. Is there easier way to apply so far. As I may over complicating the solution.

[Thom Parker]

To start, besides the bad formatting, this is not Acrobat JavaScript. If you had looked in the console window you would have seen an error reported on the first line. Something like this;

ReferenceError: XMLHttpRequest is not defined

Where did you get this code? 

See the Acrobat JavaScript reference for a list of actual objects and functions in the Acrobat JavaScript model.

 https://opensource.adobe.com/dc-acrobat-sdk-docs/library/jsapiref/index.html

[Kaxkul]

Thanks @Thom Parker, to this stage my knowedge is limited 😞

I didn't know it was that complicated. I had a problem where users download old versions and they don't check back for updates. I'm struggling with this, so I thought if something could check the name of the file with the version and alert users, that would be great. The code from a friend.

[Thom Parker]

There is a way to do this. And it's not that complicated. 

Use the doc.submitForm() function. You're server side script will need to be modified to return a data format that is acceptable to Acrobat, such as XML, XFDF, or FDF.

[Kaxkul]

Thanks, @Thom Parker  and @Bernd Alheit , for taking the time to respond to my question. I'll leave it here because I don't have enough knowledge to implement that.