xxx

var arr = [[1, 5], [10, 15], [21, 25]], tmp = [];

            arr.forEach(function (el, i) {
                var next = arr[i + 1]，
                    val = next ? next : arr[0];
                    tmp.push([el[1], val[0]]);
            })
            JSON.stringify(tmp); 

 window.devicePixelRatio zoom