Problem in Function IONIC 2 Typescript - Function executes only once

Good Night!

I have a problem with a function in Typescript (Ionic 2). The function performs a search / filter from the contents of the tags. The user enters the number they want to fetch and the function filters from the number entered. The first time the query screen is called, the function executes normally, without problem, and can even perform several searches. However, when you exit the screen and return to it for more queries, the search no longer works, it does not perform the filtering. Can anyone help solve this problem?

myFunction() {

        this.input = document.getElementById("myInput");
        this.filter = this.input.value.toUpperCase();
        this.ul = document.getElementById("myUL");
        this.li = this.ul.getElementsByTagName("li");

        for (this.i = 0; this.i < this.li.length; this.i++) 
        {
          this.a = this.li[this.i].getElementsByTagName("a")[0];

          if(this.a.innerHTML.toUpperCase().indexOf(this.filter)> -1) 
          {
              this.li[this.i].style.display = "";
          } else {
              this.li[this.i].style.display = "none";
          }
        }
  }

Thank you in advance.