Performance of ES6 features relative to the ES5 baseline operations per second (2022)

3 points by gnyeki

andyferris

It would be interesting to see results for the latest engines.

gnyeki

I found it surprising that constructs like for (var … of …) are slower than their ES5 counterparts in almost all the major browser engines. Or at least they seem to have been in 2022.

easrng

iteration is slower than property access. https://gist.github.com/easrng/5ab2f2d49309d40462054a4beca1de5c
olliej
the fundamental design of iteration is slower that the alternatives: a for loop over an array is an indexed access and integer incrementation, and in-bounds integer access of an array was optimized in all engines 20 years ago.

a for(in) loop is also faster but the reasons are because it actually gets very close to to an array loop - the set of properties to lookup are cached, and for normal property access (at least in jsc) that is functionally lowered to
```
if (structure of object == the structure of the object when the loop started)
  property_value = object->properties[current_index++]
else
  property_value = object[property_name_list[current_index++]
```
where property_name_list is the list of all the properties to visit, in the order to be visited, that is cached on the object structureid (JSC terminology for a “hidden class”), so it’s ideally calculated once.