There's a lot of discussion in the esdiscuss thread "Set length property". This was a hotly debated issue, so it's not surprising that you do not necessarily agree with the resolution.
There is a tremendous amount of arguing about this in esdiscuss. Ultimately, the argument that prevailed (as evidenced by the fact that ES2015's Sets have size
and not length
) was summarized in a post by David Bruant:
...for me 'length' refers to a measurement with something like a ruler. You start at 0 and see up to where it goes. This is very accurate for an array which is an indexed set (starting at 0 and growing) and for arrays as considered in C (continuous sequence of bytes) which ECMAScript arrays seem inspired of. This is probably less relevant for unordered collections such as sets which I'd tend to consider as a messy bag.
And further discussed in a post by Dean Landolt:
Just wanted to jump in and say non-writable length
is consistent with String behavior as well, but David makes a good point about length
implying metric topology. David's suggestion of count
is nice. ISTM what we're talking about is cardinality
, but no need to get too silly w/ precision. Though size
is just fine with me, and has plenty of prior art.