javascript timer error

Question

I started working on a timer to show how long people have been on my page. The problem is that instead of counting the seconds, it just keeps adding zeros to the end. Can anyone show me where I went wrong?

<script language="javascript">
<!--
var seconds = 0
var minutes = 0
document.getElementById('timer').innerHTML = '0'
function Timer() {
    if ( seconds < 10 ) {
        seconds = "0" + seconds
    }
    else if ( minutes < 10 ) {
        minutes = "0" + minutes
    }
    else if ( seconds >= 59 ){
        seconds = 0
        minutes += 1
    }
    else
        seconds += 1
        document.getElementById('timer').innerHTML = "You've been on my blog for    "+minutes+" : "+seconds+" minutes."
        setTimeout("Timer()",1000)
}
//-->
</script>

deceze · Accepted Answer · 2010-11-09 06:05:50Z

2

Well yes, because you're concatenating a string. The + operator does both concatenation and addition.

"0" + foo  // concatenate the string "0" and foo
0 + foo    // add foo to 0 (given that both are numbers)

You're going about the timer the wrong way though. Your script is not guaranteed to execute on time, any slight delay in execution will give you accumulative the wrong value. The right way to do a timer is to take a fixed start time and use that as the base to calculate the difference every second or so.

var start = Date.now();
function timer() {
    alert(((Date.now() - start) / 1000) + ' seconds elapsed');
}
setInterval(timer, 1000);

edited Nov 9, 2010 at 6:05

answered Nov 9, 2010 at 4:54

deceze♦

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3 Comments

zzzzBov Over a year ago

you beat me to it. only going to add that parseInt() will get you an int val from a string if necessary.

Tommy Over a year ago

But I'm adding a leading zero to the seconds and minutes until they pass ten, so instead of, for example five minutes and three seconds being 5:3, it will be 05:03, wouldn't it have to be a string for that?

deceze Over a year ago

@Tommy First you need to keep track of the numeric value correctly. Formatting the time with leading zeros is a separate issue.

Larry K · Accepted Answer · 2010-11-09 04:54:39Z

0

You're switching the variable type for seconds from being:

var seconds = 0  // integer type
....
seconds = "0" + seconds // now seconds is holding a string!

seconds (and minutes) should only be integers.

Also, just focus on the seconds. Later, divide it by 60 to display number of minutes. seconds % 60 will be the remaining number of sec.

answered Nov 9, 2010 at 4:54

Larry K

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