A more efficient alternative for CLJS str that emits optimizable JS code. Fully compatible with older versions of JS.

(ns borkdude.cljs-str
  (:refer-clojure :exclude [str])
  (:require [borkdude.cljs-str :refer [str])))

(str 1 2 3)

The CLJS str that comes with this library emits code that can be optimized by JavaScript engines. In some cases, especially when you use constant values, e.g. (str "foo" "bar"), it can be -300x faster due to emitting code which can be easily folded into a constant string. With using variables, e.g. (str "foo" x y z), this version is still about 4x faster due to avoiding allocating arrays.

This test illustrates the gain in performance:

(defn str-test
  (let [f1 (fn [] (str 1 2 nil (+ 1 2 3)))
        f2 (fn [] (clojure.core/str 1 2 nil (+ 1 2 3)))]
    (simple-benchmark [] (f1) 100000000)
    (simple-benchmark [] (f2) 100000000)))

[], (f1), 100000000 runs, 31 msecs
[], (f2), 100000000 runs, 8982 msecs

When using str at runtime, e.g. in (apply str [1 2 3]), borkdude.cljs-str/str falls back on cljs.string/join which is just as fast as when using str with apply.

Yes, already in progress here.

MIT