opt: formatToJSFunc use string plus

[somnus-L]

Development guide

Link

Test on local before making the PR

go run ./lib/utils/simple-check

when I use pprof analyze memory , I found this :

so, I use string plus instead fmt.Sprintf

[ysmood]

If you want extreme performance, you can even use a sync.Pool here to reduce memory allocation and deallocation overhead.