What is the fastest way to create a union of many polygons in turfjs? - turfjs

Question

I have something like this but with large sets it's awfully slow:
let unionize = (triangles) => {
if(triangles.length == 0) {
return null
}
let ret = triangles[0].feature
triangles.forEach((t, index) => {
if(index > 0) {
ret = turf.union(t, t)
}
})
return ret
}

Answer 1

featureEach tends to be faster than a trivial array forEach although with more features the gain decreases.
<script src="https://cdn.jsdelivr.net/npm/#turf/turf#5.1.6/turf.min.js"></script>
<script>
const generateGrid = (cellSide = 100, units = "kilometers") => {
const bbox = [-95, 30, -85, 40];
return turf.triangleGrid(bbox, cellSide, {
units
});
}
const unionizeForEach = (triangles) => {
console.time('unionizeForEach');
if (triangles.length == 0) {
return null
}
let ret = triangles[0];
triangles.forEach((t, index) => {
if (index > 0) {
ret = turf.union(ret, t)
}
});
console.timeEnd('unionizeForEach');
return ret
}
const unionizeFeatureEach = (triangles) => {
console.time('unionizeFeatureEach');
if (triangles.features.length === 0) {
return null
}
let ret = triangles.features[0];
turf.featureEach(triangles, function (currentFeature, featureIndex) {
if (featureIndex > 0) {
ret = turf.union(ret, currentFeature)
}
});
console.timeEnd('unionizeFeatureEach');
return ret;
}
[100, 50, 10].map(cellSide => {
const triangleGrid = generateGrid(cellSide, 'kilometers');
console.info(`triangleGrid has ${triangleGrid.features.length} features`);
const union_foreach = unionizeForEach(triangleGrid.features);
const union_featureeach = unionizeFeatureEach(triangleGrid);
console.assert(JSON.stringify(union_foreach) === JSON.stringify(union_featureeach));
console.log('\n---\n');
})
</script>