JavaScript - calculate weighted color between indicated colors

const calculateWeightedColor = (colors, weights) => {

    if (colors.length !== weights.length) {

        throw new Error('Values and weights arrays must have same size.');

    }

    let r = 0, g = 0, b = 0; // sums of components

    let s = 0;               // sum of weights

    for (let i = 0; i < colors.length; ++i) {

        const color = colors[i];

        const weight = weights[i];

        r += weight * color.red;

        g += weight * color.green;

        b += weight * color.blue;

        s += weight;

    }

    return {

        red:   Math.round(r / s),

        green: Math.round(g / s),

        blue:  Math.round(b / s)

    };

};

​

​

// Example helpers:

​

const appendColor = (color) => {

    const element = document.createElement('div');

    element.style.display = 'inline-block';

    element.style.width = '20px';

    element.style.height = '20px';

    element.style.background = `rgb(${color.red}, ${color.green}, ${color.blue})`;

    document.body.appendChild(element);

};

​

const appendSpace = (size) => {

    for (let i = 0; i < size; ++i) {

        document.body.appendChild(document.createElement('br'));

    }

};

​

​

// Example input:

​

const colors = [

    {red:  23, green:  23, blue: 230},

    {red:  23, green: 230, blue: 229},

    {red:  23, green: 230, blue:  27},

    {red: 229, green: 230, blue:  23},

    {red: 230, green:  23, blue:  23}

];

​

​

// Usage example 1:

​

const color = calculateWeightedColor(colors, [1, 0, 0, 0, 0]);

​

console.log(`{red: ${color.red}, blue: ${color.green}, green: ${color.blue}}`);

​

​

// Usage example 2:

​

for (let i = 0; i < colors.length; ++i) {

    appendColor(colors[i]); // displays input colors

}

​

appendSpace(2);

​

appendColor(calculateWeightedColor(colors, [1, 0, 0, 0, 0]));

appendColor(calculateWeightedColor(colors, [1, 1, 0, 0, 0]));

appendColor(calculateWeightedColor(colors, [1, 1, 1, 0, 0]));

appendColor(calculateWeightedColor(colors, [1, 1, 1, 1, 0]));

appendColor(calculateWeightedColor(colors, [1, 1, 1, 1, 1]));

​

appendSpace(1);

​

appendColor(calculateWeightedColor(colors, [1,    2,   4, 0, 0]));

appendColor(calculateWeightedColor(colors, [0.25, 0.5, 1, 0, 0]));  // the same like [1, 2, 4, 0, 0]

​

appendSpace(1);

​

appendColor(calculateWeightedColor(colors, [0.5, 0, 0, 0, 0.7]));