blob: 530e21e818891d80f7b6c925bf5c7343a03de119 [file] [log] [blame]
module.exports = function(arr, start, end, step) {
if (typeof start == 'string') throw new Error("start cannot be a string");
if (typeof end == 'string') throw new Error("end cannot be a string");
if (typeof step == 'string') throw new Error("step cannot be a string");
var len = arr.length;
if (step === 0) throw new Error("step cannot be zero");
step = step ? integer(step) : 1;
// normalize negative values
start = start < 0 ? len + start : start;
end = end < 0 ? len + end : end;
// default extents to extents
start = integer(start === 0 ? 0 : !start ? (step > 0 ? 0 : len - 1) : start);
end = integer(end === 0 ? 0 : !end ? (step > 0 ? len : -1) : end);
// clamp extents
start = step > 0 ? Math.max(0, start) : Math.min(len, start);
end = step > 0 ? Math.min(end, len) : Math.max(-1, end);
// return empty if extents are backwards
if (step > 0 && end <= start) return [];
if (step < 0 && start <= end) return [];
var result = [];
for (var i = start; i != end; i += step) {
if ((step < 0 && i <= end) || (step > 0 && i >= end)) break;
result.push(arr[i]);
}
return result;
}
function integer(val) {
return String(val).match(/^[0-9]+$/) ? parseInt(val) :
Number.isFinite(val) ? parseInt(val, 10) : 0;
}