A workaround to detecting if a native app is installed on the hosting mobile device.

index.html

<button id="btn1">Open Facebook app</button>

nativelink.js

var NativeLink = new function() {
    var iframe, openTime, downloadLink, timeoutDelay = 300;
    
    function init() {
        // create iframe amd hide it
        iframe = document.createElement("iframe");
        iframe.style.visibility = "hidden";
        iframe.style.position = "absolute";
        document.body.appendChild(iframe);
    }
 
    this.open = function(native, download) {
        downloadLink = download;
        openTime = new Date().getTime();
        iframe.src = native;
        setTimeout(onTimeout, timeoutDelay);
    };
 
    function onTimeout() {
        var now = new Date().getTime();
        if (now - openTime < 500) {
            window.location.href = downloadLink;
        }
    }
 
    init();
};

usage.js

// define links
var native = "fb://",
    download = "https://itunes.apple.com/en/app/facebook/id284882215";
 
// attach listener
var btn1 = document.getElementById("btn1");
btn1.addEventListener("click", function() {
    NativeLink.open(legitNative, download);
});