As far as I know, V8 Javascript engine makes double number conversion (to i32 and back) to perform bit operation. Let's consider next example:
const int32 = new Int32Array(2);
int32[0] = 42;
int32[1] = 2;
const y = int32[0] | int32[1];
Does V8 makes double conversion in this case ? If no, does it mean bit operations are faster on Int32Array values?
UPDATE: By double conversion I mean: from 64 bit (53 bits precision) to -> 32bit and again to -> 64 bit
V8 developer here. The short answer is: there are no conversions here, bitwise operations are always performed on 32-bit integers, and an Int32Array also stores its elements as 32-bit integers.
The longer answer is "it depends". In unoptimized code, all values use a unified representation. In V8, that means number values are either represented as a "Smi" ("small integer") if they are in range (31 bits including sign, i.e. about -1 billion to +1 billion), or as "HeapNumbers" (64-bit double with a small object header) otherwise. So for an element load like int32[0], the 32-bit value is loaded from the array, inspected for range, and then either tagged as a Smi or boxed as a HeapNumber. The following | operation looks at the input, converts it to a 32-bit integer (which could be as simple as untagging a Smi, or as complex as invoking .valueOf on an object), and performs the bitwise "or". The result is then again either tagged as a Smi or boxed as a HeapNumber, so that the next operation can decide what to do with it.
If the function runs often enough to eventually get optimized, then the optimizing compiler makes use of type feedback (guarded by type checks where necessary) to elide all these conversions that are unnecessary in this case, and the simple answer will be true.