immutable-js/src/Range.js

Immutable types in JavaScript

/**
 *  Copyright (c) 2015, Jan Biasi.
 *  All rights reserved.
 *
 *  This source code is licensed under the BSD-style license found in the
 *  LICENSE file in the root directory of this source tree. An additional grant
 *  of patent rights can be found in the PATENTS file in the same directory.
 */

import { IndexedSequence } from './Sequence';
import { NativeArray, isNative } from './Native';
import { invariant } from './util/toolset';

export class Range extends IndexedSequence {
    constructor(start, end, step) {
        if(!(this instanceof Range)) {
            return new Range(start, end, step);
        }
        invariant(step !== 0, 'Can\'t create a range with steps by 0');
        start = start || 0;
        if(end === undefined) {
            end = Infinity;
        }
        step = step === undefined ? 1 : Math.abs(step); // Absolute value of number
        if(end < start) {
            step = -step;
        }
        this.__start = start;
        this.__end = end;
        this.__step = step;
        this.size = Math.max(0, Math.ceil((end - start) / step - 1) + 1);
        if(this.size === 0) {
            if(EMPTY_RANGE) {
                return EMPTY_RANGE;
            }
            EMPTY_RANGE = this;
        }
    }
}

var EMPTY_RANGE;