Object Descriptors & Property Flags

What values appear when manipulating a sealed object?

const obj = { a: 1, b: 2 };
Object.seal(obj);

obj.a = 3;    // Change existing property
obj.c = 4;    // Add new property
delete obj.b; // Delete property

console.log(obj.a, obj.b, obj.c);

3, 2, 4
3, 2, undefined
The console will log '3, 2, undefined' because Object.seal(): 1) Makes all properties non-configurable, preventing deletion, 2) Prevents adding new properties to the object, 3) Allows modifying values of existing properties (they remain writable), 4) The value of 'a' was successfully changed to 3, 5) The attempt to delete 'b' failed silently (in non-strict mode), so it remains 2, 6) The attempt to add property 'c' failed silently, so it's undefined, 7) Object.seal() is useful when you want to prevent structural changes while allowing value updates.
1, 2, undefined
1, 2, 4

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