app.js

/**
 * Variable initialization.
 */
 var charsPerKeyStroke = 5;
 var startIndex = 0;
 var endIndex = 0;
 var sourceCode = "";
 var sourceElement;
 var sourceContainer;
 var fileName = "code.txt";
 var cursorChar = "|";
 
 /**
  * Gets the contents which will appear as the user types or taps.
  */
 function getFileContents() {
     var rawFile = new XMLHttpRequest();
     rawFile.onreadystatechange = function () {
         if (rawFile.readyState === 4) {
             if (rawFile.status === 200 || rawFile.status === 0) {
                 sourceCode = rawFile.responseText;
                 console.log(sourceCode);
             }
         }
     };
     rawFile.open("GET", fileName, true);
     rawFile.send();
 }
 
 /**
  * Gets the areas which will be updated on each keystroke or tap.
  */
 function getElements() {
     sourceContainer = document.getElementById("container");
     sourceElement = document.getElementById("source");
 }
 
 /**
  * Initializes variables and creates blinking cursor effect.
  */
 function init() {
     getFileContents();
     getElements();
     window.setInterval(updateCursor, 500);
 }
 
 /**
  * Updates cursor position on each keystroke or tap.
  */
 function updateCursor() {
     var text = sourceElement.textContent;
     var lastChar = text.charAt(text.length-1);
     if (lastChar === cursorChar) {
         sourceElement.textContent = text.substring(0,text.length-1);
     }
     else {
         sourceElement.textContent += cursorChar;
     }
 }
 
 /**
  * Sets updated code.
  */
 function updateScreen() {
     endIndex += charsPerKeyStroke;
     sourceElement.textContent = sourceCode.substring(startIndex, endIndex);
 }
 
 /**
  * Updates scroll position to match code's height.
  */
 function updateScrollPosition() {
     window.scrollTo(0, sourceContainer.scrollHeight);
 }
 
 /**
  * Updates all states.
  */
 function update() {
     updateScreen();
     updateScrollPosition();
 }
 
 /**
  * Runs application.
  */
 function run() {
     window.onload = init;
     window.onkeydown = update;
     window.ontouchstart = update;
 }
 
 run();