Get a variable to count up/down on keyboard press in JavaScript

Question

I am trying to get a count from 100 to count up/down by 1 when a keyboard button is pressed. I am currently using the keys 8 and 2 on the keypad which correspond to 104 and 98 ascii numbers.

At the moment the code I am using counts down but I cannot get it to count up on 104 key press.

What am I missing.

var keyY = 100;

document.addEventListener('keydown', function(event){
  var keyPressed = event.keyCode;
  switch(keyPressed){
    case 104:
      keyY = keyY + 1;
    case 98:
      keyY = keyY - 1;
  }
  console.log('key pressed: ' + keyPressed);
  console.log('keyX = ' + keyY);
});

<html>
  <head>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
  </head>
  <body>
      <script src="index.js"></script>
  </body>
</html>

Check the syntax for a switch statement carefully: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — ADyson
– ADyson, Commented Dec 9, 2019 at 10:08

Refilon · Accepted Answer · 2019-12-09 10:10:58Z

5

You're missing the break, which is very important.

The optional break statement associated with each case label ensures that the program breaks out of switch once the matched statement is executed and continues execution at the statement following switch. If break is omitted, the program continues execution at the next statement in the switch statement.

From here

var keyY = 100;

document.addEventListener('keydown', function(event){
  var keyPressed = event.keyCode;
  switch(keyPressed){
    case 104:
      keyY++;
    break;
    case 98:
      keyY--;
    break;
  }
  console.log('key pressed: ' + keyPressed);
  console.log('keyX = ' + keyY);
});

EDIT: use keyY++; instead of keyY = keyY + 1; & keyY--; instead of keyY = keyY - 1;

edited Dec 9, 2019 at 10:10

answered Dec 9, 2019 at 10:06

Refilon

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3 Comments

Giovani Vercauteren Over a year ago

Just a little extra I would like to add, but it's totally not necessary, is using keyY++ or keyY--

user2669997 Over a year ago

Thanks, i was using Y++ and Y-- and have used Switch a few times, can't believe I missed the break, been annoying me all morning, such a silly mistake. thank you for getting me back on track

Refilon Over a year ago

@GiovaniVercauteren I added it to the answer. Thank you for the improvement.Steve8428 No problem. Sometimes that happens to me too ;)

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