Javascript array chunk

array_chunk.js

// Splits an array into equal sized chunks
Array.prototype.chunk = function(pieces) {
  pieces = pieces || 2;
  var len = this.length;
  var mid = (len/pieces);
  var chunks = [];
  var start = 0;
  for(var i=0;i<pieces;i++) {
    var last = start+mid;
    if (!len%pieces >= i) {
      last = last-1
    }
    chunks.push(this.slice(start,last+1) || []);
    start = last+1;
  }
  return chunks;
}