Javascript to randomly add/subtract to a number every second

Question

What I want my function to achieve for my javascript function is for every second to either randomly subtract or add (a random number) to a number held in a div.

Here's what I have so far.

It doesn't work, it seems to append the number to the end of the div value (100), and also it doesn't take into account that I want it to either randomly add or subtract (it just adds at the moment)

    setInterval(function(){
        random = (Math.floor((Math.random()*15)+1)); 
        currentnumber = document.getElementById('number');

        document.getElementById('number').innerHTML =  currentnumber + random;

     }, 1000);

`currentnumber` should probably be `.innerHTML` and not the element itself. — bozdoz, Jan 21 '14 at 23:46
Maybe you could try currentnumber = parseInt(document.getElementById('number').innerHTML); ? (edit: yes innerHTML is what you're after, otherwise you're manipulating the DOM object) — Dan H, Jan 21 '14 at 23:46
For the record, this question was a clear oversight of missing `innerHTML` when declaring the variable. — bozdoz, Jan 22 '14 at 04:14

Rooster · Accepted Answer · 2014-01-21T23:58:08.577

7

parse the current value as an integer, and then do another math.random and use it to decide negative or positive. Lastly, you need to use the innerHTML of currentnumber, not the entire node. So something like this should work:

setInterval(function(){
    random = (Math.floor((Math.random()*15)+1));
    var plusOrMinus = Math.random() < 0.5 ? -1 : 1;
    random = random * plusOrMinus; 
    currentnumber = document.getElementById('number');

    document.getElementById('number').innerHTML =  parseInt(currentnumber.innerHTML) + random;

 }, 1000);

WORKING FIDDLE

edited Jan 21 '14 at 23:58

answered Jan 21 '14 at 23:49

Rooster

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post the fiddle, I'm sure you're using more code than what you posted – Rooster Jan 21 '14 at 23:53
@JuergPodolski added working fiddle. you needed to also use the innerhtml of currentnumber besides just parsing it as an integer. – Rooster Jan 21 '14 at 23:58
Nice! Thanks Rooster much appreciated. – J. Podolski Jan 22 '14 at 00:00

score 1 · Answer 2 · edited May 23 '17 at 11:52

1

.innerHTML returns you a string which you'll need to parse into an integer to perform the addition or subtraction. Have a look at a number of methods listed in the following SO question

How do I convert a string into an integer in JavaScript?

edited May 23 '17 at 11:52

Community

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answered Jan 21 '14 at 23:49

Ani

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score 1 · Answer 3 · answered Jan 21 '14 at 23:59

currentnumber is a DOM object, and you can't add that to a number.

var div = document.getElementById('number');
div.innerHTML = Number(div.innerHTML) + 3;

Notice you are getting the innerHTML of the div, converting that to a Number(), adding your random number to it, and THEN setting your div.innerHTML to your new value.

http://jsfiddle.net/9LqQG/1/

score 0 · Answer 4 · answered Jan 21 '14 at 23:49

Maybe try something like this:

setInterval(function(){
    random = (Math.floor((Math.random()*15)+1)); 
    currentnumber = parseInt(document.getElementById('number').innerHTML);

    document.getElementById('number').innerHTML =  currentnumber + random;
 }, 1000);

Your currentnumber variable needs to get the innerHTML of the element, then parse the string into an integer.

jsFiddle

Javascript to randomly add/subtract to a number every second

4 Answers4