const encoded = "qospGlrrB";

function safeDecodePolyline(encoded) {
    let index = 0, len = encoded.length;
    let lat = 0, lng = 0;
    const poly = [];

    while (index < len) {
        let b, shift = 0, result = 0;
        do {
            if (index >= len) break;
            b = encoded.charCodeAt(index++) - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        let dlat = ((result & 1) !== 0 ? ~(result >> 1) : (result >> 1));
        lat += dlat;

        shift = 0;
        result = 0;
        do {
            if (index >= len) break;
            b = encoded.charCodeAt(index++) - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        let dlng = ((result & 1) !== 0 ? ~(result >> 1) : (result >> 1));
        lng += dlng;

        poly.push([lat / 1e5, lng / 1e5]);
    }
    return poly;
}

const pts = safeDecodePolyline(encoded);
console.log("Decoded", pts.length, "points.");
for(let i=0; i<5 && i<pts.length; i++) {
    console.log(pts[i]);
}
if(pts.length > 5) {
    console.log("...");
    for(let i=pts.length-5; i<pts.length; i++) {
        console.log(pts[i]);
    }
}