3 ms·

Does spreading arrays come with a performance penalty?

• spicebox 3y ago
  Spreading an array requires looping over all the array elements which is O(n) compared to something like Array.push() which is just 0(1), although spreading has other benefits like copying rather than mutating
• dexwiz 3y ago
  Spreading allocates a new array. Most things you can do with spread you can do with normal functions that either just directly access an entry or mutate an array directly. [first, …rest] is nice, but will always be slower than direct access.
• dceddia 3y ago
  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).