Practice Set, Week 9, Keyboard Events

by Tanveer Khan

HTML

<h3>Practice Set, Week 9, Keyboard Events</h3>

<p>This page contains a box with a "puck" in it. The javascript contains functions that will move the puck in each of four directions. Your task is to write an event handler that will respond to the keyboard - specifically, to allow the user to use the arrow
  keys to move the puck around.</p>
<p>You can attach an event handler to the window object, and have a conditional to see which key was pressed. The <a href="http://jsfiddle.net/cscie3/j1uLsvay/">keyCode utility</a> we referred to in Week 9, lesson 3 of the course may be helpful to you.</p>
<p>Also, when running your code in JSFiddle, you will have to give this HTML output frame focus (by clicking on it once) for your code to capture keyboard activity. </p>
<p>Hint - all you have to do is listen for keydown or keyup, and depending on which arrow key was pressed, call the appropriate function. </p>
<div id="container">
  <div id="output"></div>
  <div id="puck"></div>
</div>

CSS

#container {
  height: 200px;
  width: 400px;
  border: 1px solid black;
  background-color: #dddddd;
}

#puck {
  border: 1px solid red;
  height: 20px;
  width: 20px;
  background-color: red;
  position: relative;
  top: 90px;
  left: 190px;
}

JavaScript

// Add your event handler here to listen for keyboard
//   activity and call the functions below as needed.
// https://css-tricks.com/snippets/javascript/javascript-keycodes/
window.addEventListener('keydown', keydown);

function keydown(event) {

  if (event.keyCode == 38) {
    mvup();
  } else if (event.keyCode == 39) {
    mvright();
  } else if (event.keyCode == 40) {
    mvdown();
  } else if (event.keyCode == 37) {
    mvleft();
  }
}


// initial location of the puck, and step size
var step = 4;
var pTop = 90;
var pLeft = 190;

// utility functions that will move the puck
var puck = document.getElementById("puck");

function mvup() {
  pTop -= step;
  puck.style.top = pTop + "px";
}

function mvdown() {
  pTop += step;
  puck.style.top = pTop + "px";
}

function mvleft() {
  pLeft -= step;
  puck.style.left = pLeft + "px";
}

function mvright() {
  pLeft += step;
  puck.style.left = pLeft + "px";
}