util: possible way to speed up util.format()

[estliberitas]

Hi guys. While I was looking at sources... I found that util.format() is based on String#replace() with "replacer" function.

I am wondering if anyone has experimented with automata-based solution maybe composed with String#indexOf('%') (for faster moving from one char sequence to another).

If no, would you be interested in such an implementation? I'd benchmark following impls.:

• automata w/ indexOf('%')
• automata w/o indexOf('%')

Or, explain plz why it would not give actual speedup.

[estliberitas]

I also found other issues which intend to optimize util.format():

• [WIP] lib: optimize util.format() by @bnoordhuis seems to be stalled
• util: Speed up the common case of formatting a single string. by @ChALkeR simplies common case with single string

Another one thing to consider would be concatenation of result string. Without indexOf() it's simple with just adding a char to result string (any perf. overhead here?), but with indexOf() it would either require small inner loop or substring() usage which actually gives another one called function per each gap between placeholders.

[andrasq]

It's an interesting idea, but examining a string character by character is very fast in nodejs.
I have a simple printf-like % argument interpolator (qprintf) that works as you describe
(state machine that uses indexOf to find the next %), and util.format is 2x faster. (I should
probably experiment with that, see if I can close the gap.)

[andrasq]

Walking a string character by character is faster than using indexOf.
I modified qprintf to iterate over the string instead of using indexOf and it sped up over 20%
(still using slice to concat chunks of the format string, it's faster than appending chars).

The stalled pull request might have been to help older versions of util.format.
The current (v6) version is 5-10x faster than it was in v0.10 and v4.4, see the
changes made in #5360

[evanlucas]

Going to go ahead and close since util.format is no longer using String#replace. Performance has improved pretty significantly for it since then. Thanks!