Having written one of the major HTML5 game engines (Construct 2), it's extraordinarily difficult to completely avoid memory allocations, so there is always some

Having written one of the major HTML5 game engines (Construct 2), it's extraordinarily difficult to completely avoid memory allocations, so there is always some garbage overhead. Consider straightforward calls like slice() make allocations and have to be worked around to avoid garbage - and that is very much just the tip of the iceberg.