Run results for: Clone object

Test name	Executions per second
✓ Manual clone (value)	3,286,589 Ops/sec
Manual clone (object)	3,280,484 Ops/sec
JSON Stringify+Parse	658,612 Ops/sec
JSON Stringify+Parse with top-level vars	657,576 Ops/sec
StructuredClone	441,190 Ops/sec

Script Preparation code:

var object = {
    type: "FeatureCollection",
    features: [{
            type: "Feature",
            properties: {},
            geometry: {
                type: "Point",
                coordinates: [4.483605784808901, 51.907188449679325]
            }
        },
        {
            "type": "Feature",
            "properties": {},
            "geometry": {
                "type": "Polygon",
                "coordinates": [
                    [
                        [3.974369110811523, 51.907355547778565],
                        [4.173944459020191, 51.86237166892457],
                        [4.3808076710679416, 51.848867725914914],
                        [4.579822414365026, 51.874487141880024],
                        [4.534413416598767, 51.9495302480326],
                        [4.365110733567974, 51.92360787140825],
                        [4.179550508127079, 51.97336560819281],
                        [4.018096293847009, 52.00236546429852],
                        [3.9424146309028174, 51.97681895676649],
                        [3.974369110811523, 51.907355547778565]
                    ]
                ]
            }
        }
    ]
};

var copy = null;

// v1

function deepCloneJsonValue(value) {
  if (value === null || typeof value !== "object") return value;

  if (Array.isArray(value)) return deepCloneJsonArray(value);
  return deepCloneJsonObject(value);
}

function deepCloneJsonObject(obj) {
  const cloned = { ...obj };
  for (const key in obj) {
    const value = obj[key];
    if (typeof value !== "object" || value === null) continue;
    cloned[key] = Array.isArray(value) ? deepCloneJsonArray(value) : deepCloneJsonObject(value);
  }
  return cloned;
}

function deepCloneJsonArray(arr) {
  const cloned = [];
  for (let i = 0, len = arr.length; i !== len; i++) {
    cloned.push(deepCloneJsonValue(arr[i]));
  }
  return cloned;
}

// v2

function deepCloneJsonValue2(value) {
  if (value === null || typeof value !== "object") return value;

  if (Array.isArray(value)) return deepCloneJsonArray2(value);
  return deepCloneJsonObject2(value);
}

function deepCloneJsonObject2(obj) {
  const cloned = { ...obj };
  for (const key in cloned) {
    const value = cloned[key];
    if (typeof value !== "object" || value === null) continue;
    cloned[key] = Array.isArray(value) ? deepCloneJsonArray2(value) : deepCloneJsonObject2(value);
  }
  return cloned;
}

function deepCloneJsonArray2(arr) {
  const cloned = [];
  for (let i = 0, len = arr.length; i !== len; i++) {
    cloned.push(deepCloneJsonValue2(arr[i]));
  }
  return cloned;
}

Run results for: Clone object

Manual clone

Manual clone v2