Function Problem IONIC 2 Typescript - Function runs only once

Question

Goodnight!

I have a problem with a function in Typescript(Ionic 2). The function does a search/filter from the contents of the tags. The user enters the number you want to search for and the function filters from the number entered. The first time the query screen is called, the function performs normally, no problem, and can even do several searches. However, when leaving the screen and returning to perform more queries, the search no longer works, does not perform the filtering. Can someone 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";
          }
        }
  }

Thanks in advance.