Javascript: take every nth Element of Array

Filter itself returns an array. If I'm understanding you correctly, you don't need that surrounding loop. So:

newArr = oldArr.filter(function(value, index, Arr) {
    return index % 3 == 0;
});

will set newArr to every third value in oldArr.


Maybe one solution :

avoid filter because you don't want to loop over 10 000 elements ! just access them directly with a for loop !

 
var log = function(val){document.body.innerHTML+='<div></pre>'+val+'</pre></div>'} 

var oldArr = [0,1,2,3,4,5,6,7,8,9,10]
var arr = [];

var maxVal = 5;

var delta = Math.floor( oldArr.length / maxVal );

// avoid filter because you don't want
// to loop over 10000 elements !
// just access them directly with a for loop !
//                                 |
//                                 V
for (i = 0; i < oldArr.length; i=i+delta) {
  arr.push(oldArr[i]);
}


log('delta : ' + delta + ' length = ' + oldArr.length) ;
log(arr);