Adding to the others here, yeah - it has to loop over the whole array, and it allocates a new one. The allocation itself costs something and it also creates wor

Adding to the others here, yeah - it has to loop over the whole array, and it allocates a new one. The allocation itself costs something and it also creates work for the garbage collector (freeing the old one). So it’s a lot of work compared to a .push()! Sometimes you do need the immutability aspect though, because a lot of things use referential equality for change detection (React is a big one).