Joyrider: Polygon union

const polys = [];
body.fixture.forEach(fix => {
    if (fix.polygon) {
        polys.push(fix.vertices);
    }
});

// Attempt to merge polys
// --------------------------------
// Take first poly, try to merge it with every other remaining poly.
// On success or if all fail, move to second one and repeat
// Merged polys are added to the end of the stack
// Once all polys are checked, all remaining ones cannot be merged and are the final polys

for (let checkIdx = 0;checkIdx < polys.length;checkIdx++) {
    if (!polys[checkIdx]) continue;

    const poly1 = turf.polygon([[
        ...polys[checkIdx].map(v => [v.x, v.y]),
        [polys[checkIdx][0].x, polys[checkIdx][0].y],
    ]]);

    for (let innerCheckIdx = 0;innerCheckIdx < polys.length;innerCheckIdx++) {
        if (!polys[innerCheckIdx]) continue;
        if (innerCheckIdx === checkIdx) {continue};

        const poly2 = turf.polygon([[
            ...polys[innerCheckIdx].map(v => [v.x, v.y]),
            [polys[innerCheckIdx][0].x, polys[innerCheckIdx][0].y],
        ]]);

        try {
            const union = turf.union(poly1, poly2);

            if (union.geometry.type !== 'MultiPolygon') {
                // Merge was a success!
                polys.push(union.geometry.coordinates[0].map(v => ({ x: v[0], y: v[1] })));
                polys[checkIdx] = undefined;
                polys[innerCheckIdx] = undefined;
                break;
            }
        } catch(e) {}
    }
}

const finalPolys = polys.filter(p => typeof p !== 'undefined');