What's the difference between Object.seal() and Object.preventExtensions()?
The key difference is in how they affect existing properties: 1) Both methods prevent adding new properties to an object, 2) Object.preventExtensions() only prevents extensions - adding new properties, 3) Object.seal() additionally makes all existing properties non-configurable, 4) With seal(), properties can't be deleted or have their descriptors changed, 5) With preventExtensions(), properties remain configurable unless explicitly changed, 6) Both methods allow changing values of existing properties, 7) seal() is more restrictive, providing greater protection against structural changes to an object.