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