calculateQuantity-test.js

import calculateQuantity from '../calculateQuantity';

const quantity = {
    1920: 10,
    1366: 8,
    1024: 4,
    1280: 6
};

describe('calculateQuantity function', () => {
    it('should return maximum value', () => {
        expect(calculateQuantity(quantity, 1980)).to.equal(10);
    });

    it('should return minimum value', () => {
        expect(calculateQuantity(quantity, 960)).to.equal(4);
    });

    it('should return value from range', () => {
        expect(calculateQuantity(quantity, 1300)).to.equal(6);
    });

    it('should return value with eqal width', () => {
        expect(calculateQuantity(quantity, 1024)).to.equal(4);
        expect(calculateQuantity(quantity, 1280)).to.equal(6);
        expect(calculateQuantity(quantity, 1366)).to.equal(8);
        expect(calculateQuantity(quantity, 1920)).to.equal(10);
    });
});

calculateQuantity.js

import { last } from 'lodash';

export default function calculateQuantity(quantityObject, width) {
    const sortedValues = Object.keys(quantityObject)
        .map(key => Number(key))
        .sort((a, b) => (b - a));

    const currentWidth = sortedValues.find(value => {
        return width >= value;
    });

    return quantityObject[currentWidth || last(sortedValues)];
}