Javascript to change website favicon if specific text is present

I am trying to change the icon on the Nested tab of the Google Inbox tab. so I know which tab is at a glance.

I know there are probably extensions for this, but I'm learning Javascript and trying to go myself. I can change other icons using the "url.indexOf" command, but the Inbox page does not change the URL. So I figured I would write Javascript to find the word "Pinned" and then the Favicon change action if found. This is what I have:

    favico = function() {

    this.is_changed = 0;
    this.retry = 1000;
    this.timerFindButtons = null;
    this.list = [
        "foo",
        "bar"
        ];
}

favico.prototype.init = function(){
    setTimeout(this.looping.bind(this), this.retry);
}
favico.prototype.looping  = function(){

    var head = document.getElementsByTagName('head')[0];
    var links = head.querySelectorAll('link');


    var eles = document.querySelectorAll("div");    


    for(var ii=0;ii<eles.length;ii++){
        var foo = eles[ii].getAttribute('jstcache');
        if(foo != null && foo.indexOf('1683') != -1){
            var bar = eles[ii].innerText;
            if(bar.indexOf('Pinned') != -1){
                links[0].setAttribute('href', 'data:image/x-icon;base64,...');
                this.is_changed = 1;}



             else {
                this.is_changed = 0;
                links[0].setAttribute('href', '//ssl.gstatic.com/bt/C3341AA7A1A076756462EE2E5CD71C11/ic_product_inbox_16dp_r2_2x.png');}
        }
    }

    setTimeout(this.looping.bind(this), this.retry);
}


  var oo = new favico()
  oo.init();

      

        
        
        
      

    

What am I doing wrong? Many thanks to everyone who can help!