SetTimeout inside self function only do one loop

Question

Hi I have the following function:

Main.prototype.checkProcess = function () {

        var $this = this;

        if (document.cookie.indexOf("process=done") != -1) {

            // close the active window
            $('#processModal').modal('hide');

            document.cookie = "process=; expires=Thu, 01 Jan 1970 00:00:00 UTC; path=/;";

            return;
        }

        $this.$timer = setTimeout($this.checkProcess, 1000);

    },

I have a timer every 1000 seconds that calls again the same function but it works only the first time, after that the function is never called again.

Any clue?