A JSON array is just a JavaScript array, so you can use push and slice.
Here's an example:
var productList = [1,2,3,4,5,6,7,8,9,0]
var piecesProuducts = []
for (var i = 0; i <= 4; i++)
{
piecesProuducts.push(productList.slice(i*2, i*2+2));
}
console.log(piecesProuducts)