text: (function(window){
  
  //establish globals
  var screenContent = "";
  var calculatorScreen = document.getElementById("screen");
  var toScreenButtons = document.getElementsByClassName("to-screen");
  var clearButton = document.getElementsByClassName("clear")[0];
  var equalsButton = document.getElementsByClassName("equals")[0];
  
  //number button listener
  var i;
  for(i = 0; i < toScreenButtons.length; i++) {
      toScreenButtons[i].addEventListener("click", function(event) {
          event.preventDefault();
          screenContent += this.value;
          console.log(screenContent);
          calculatorScreen.value = screenContent;
      });
  }
  
  //clear button listener
  clearButton.addEventListener("click", function(event) {
          event.preventDefault();
          screenContent = "";
          console.log(screenContent);
          calculatorScreen.value = screenContent;
  });
  
  //equals button listener
  equalsButton.addEventListener("click", function(event) {
          event.preventDefault();
          var result = eval(screenContent);
          calculatorScreen.value = result;
  
  });
  
  })(window);
  