Displaying warning message if user is not on chrome

I am currently building a website, and I do not have the skills to make the website work on all on all browsers. So I have written a quick bit of JavaScript to detect the browser. I do not know JavaScript very well so the code does not work.

Here is the code

if(userAgent.not(/chrome/i)){
    alert("Warning.n " +
        "You are not on a recomended browser, n ciertain features might not work " +
        "try using chrome");
}

can you please just make the warning only appear if you are not using chrome.

thank you very much