Maps polygon coordinates encoder/decoder

coordintas-encode.js

export default class CoordinatesEncoder {
    static SCALE = 1000000;

    static encode(polygons) {
        const result = [];

        const intToCodes = (number) => {
            const result = [];
            for (let i = 0; i < 4; i++) {
                result[i] = 255 & (number >> 8 * i); // eslint-disable-line no-bitwise
            }
            return result;
        };

        for (const polygon of polygons) {
            let charCodes = [];
            let previous = [0, 0];
            for (let [x, y] of polygon) {
                x = x * this.SCALE - previous[0];
                y = y * this.SCALE - previous[1];
                previous = [x + previous[0], y + previous[1]];
                charCodes = charCodes.concat(intToCodes(x), intToCodes(y));
            }
            result.push(charCodes);
        }

        const encodeCharCodes = (charCodes) => {
            return btoa(String.fromCharCode(...charCodes)).replace(/\//g, '_').replace(/\+/g, '-');
        };

        return result.map(encodeCharCodes).join(';');
    }

    static decode(string) {
        return string.split(';').map((component) => {
            component = atob(component.replace(/_/g, '/').replace(/-/g, '+'));
            const points = [];
            let last = [0, 0];
            for (let i = 0; i < component.length; i += 8) {
                let lat = 0;
                let lng = 0;
                const part = component.substr(i, 8);
                for (let j = 0; j < 4; j++) {
                    lat |= part.charCodeAt(j) << 8 * j; // eslint-disable-line no-bitwise
                    lng |= part.charCodeAt(j + 4) << 8 * j; // eslint-disable-line no-bitwise
                }
                const point = [Number(((lat / this.SCALE) + last[0]).toFixed(6)), Number(((lng / this.SCALE) + last[1]).toFixed(6))];
                last = point;
                points.push(point);
            }

            return points;
        });
    }
}

// test
let encoded = 'dJGjAREYNgPFEQAA6_P__5UOAACCCQAAEikAAAYIAABDLQAAhRIAAA4KAADhAQAArgIAALcIAAAY8___HAkAANsDAADIAQAAa_H__xkKAACZ8___xvj__weu___n4P__GvT___Lw__8=';

let decoded = CoordinatesEncoder.decode(encoded);
let encoded2 = CoordinatesEncoder.encode(decoded);
console.log(encoded === encoded2);