unable to iterate on HtmlCollection

I have an issue with a simple code

    var x = document.getElementsByTagName("th");
    var plop = Array.prototype.slice(x);
    console.log(x);
    console.log(x.length);
    console.log(plop);

output

[item: function, namedItem: function]
0: th.fc-day-header.fc-sun.fc-widget-header.fc-first
1: th.fc-day-header.fc-mon.fc-widget-header
2: th.fc-day-header.fc-tue.fc-widget-header
3: th.fc-day-header.fc-wed.fc-widget-header
4: th.fc-day-header.fc-thu.fc-widget-header
5: th.fc-day-header.fc-fri.fc-widget-header
6: th.fc-day-header.fc-sat.fc-widget-header.fc-last
length: 7__proto__: HTMLCollection
    controller.js:309 0
    controller.js:310 []

Why does I see lenght 7 here and the x.length gives 0 ?

Thanks in advance

update : I set the code in

$scope.$on('$viewContentLoaded', function(){
}

And it works now. I'm not yet able to set an onclick method but it progress ^^