How to get a constant variable of array

hi i hav an array named contents [i] where i wanna get every 3rd value out of it.below i make an example:

contents [i] = [2,4,6,8,10,12,14,16,18];

i wanna find a script dat could return every third value which is 3,6,9
so any1 noe how to do it? thanks

Try this:-

<script type = "text/javascript">
var contents = [2,4,6,8,10,12,14,16,18,21];
var result = [];
var count = 0;
for (var i = 2; i<contents.length; i= i+3) {
result[count] = contents[i];
count++;
}

alert (result); // 6,12,18
</script>


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