/**
 * Returns an array with arrays of the given size.
 *
 * @param myArray {Array} Array to split
 * @param chunkSize {Integer} Size of every group
 */
function chunkArray(myArray, chunk_size){
    var results = [];

    while (myArray.length) {
        results.push(myArray.splice(0, chunk_size));
    }

    return results;
}

// Split in group of 3 items
var result = chunkArray([1,2,3,4,5,6,7,8], 3);
// Outputs : [ [1,2,3] , [4,5,6] ,[7,8] ]
console.log(result);