Heads or Tails program Endless loop error

Question

3.00/5 (1 vote)

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I am trying to write a simple Heads or tails program, just to practice Javascript.
Here is the code I have so far:

JavaScript

var keys = [];
var choice = Math.random();
window.addEventListener('keydown',function(e){
  keys[e.keyCode] = true;
},false);

window.addEventListener('keyup',function(e){
  delete keys[e.keyCode];
},false);

function main(){
  if (keys[38]){
    flip();
  }
}

function flip(){
  if(choice <0.51){
    document.write('Heads');
    choice = Math.random();
  }else{
    document.write('Tails');
    choice = Math.random();
  }
}

setInterval(function(){
  main();
},1000/30);

It works, and writes either heads or tails to the screen, however it is continuous, and doesn't stop writing to the screen. I wan't it to write the answer once every time you press the up key, rather than it endlessly writing either heads or tails across the screen.

Posted 8-Aug-14 3:20am

Corrigan_sam

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Comments

Sergey Alexandrovich Kryukov 8-Aug-14 14:05pm

To start with, what's the scope of this script ("body" element of HTML, "head" element, something else), what function is triggered in first place.
—SA

2 solutions

Solution 1

Not only there are no infinite loops, there are no loops at all in your code. What you see is expected behavior, because your setInterval call explicitly define that main should be called periodically with the period of 1000/30.

—SA

Posted 8-Aug-14 8:07am

Sergey Alexandrovich Kryukov

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Peter Leow · Accepted Answer · 2014-08-08T18:39:00

Try this:

XML

<!DOCTYPE html>
<html>
<body>
<div id="result">Good Luck!</div>

<script>
var placeHolder = document.getElementById('result');

var listener = window.document.addEventListener('keydown', function(e){
       if (e.keyCode == 38) flip();
    }, false);

function flip(){
var choice = Math.random();
   if(choice < 0.51){
      placeHolder.innerText = 'Heads';
   } else {
      placeHolder.innerText = 'Tails';
   }
}

</script>
</body>
</html>