building.cljs 时如何在编译时定义目标环境？

Question

I want to compile my .cljs file for both browser and node.js environments, to get server side rendering. As I understand, there's no way to define cljs env in compile time with reader macro conditions like:

#?(:clj ...)
#?(:cljs ...)

so, I can't easily tell compiler to process something like #?(:cljs-node...) in node.js env.

Second option I see here is to develop a macro file which will define env at compile time. But how to define that current build is targeting node.js? May be, I could pass some params somehow to compiler or get :target compiler param?

Here are my boot files:

application.cljs.edn:

{:require  [filemporium.client.core]
 :init-fns [filemporium.client.core/init]} 

application.node.cljs.edn:

{:require [filemporium.ssr.core]
 :init-fns [filemporium.ssr.core/-main]
 :compiler-options
 {:preamble ["include.js"]
  :target :nodejs
  :optimizations :simple}}

Answer 1

I am not aware of a public API to achive this. However, you might use cljs.env/*compiler* dynamic var in your macro to check the target platform (ie NodeJS vs browser) configured with :target in your :compiler-options and either emit or suppress the code wrapped in the macro:

(defn- nodejs-target?
  []
  (= :nodejs (get-in @cljs.env/*compiler* [:options :target])))

(defmacro code-for-nodejs
  [& body]
  (when (nodejs-target?)
    `(do ~@body)))

(defmacro code-for-browser
  [& body]
  (when-not (nodejs-target?)
    `(do ~@body)))

(code-for-nodejs
  (def my-variable "Compiled for nodejs")
  (println "Hello from nodejs"))

(code-for-browser
  (def my-variable "Compiled for browser")
  (println "Hello from browser"))

Answer 2

Here is up to date code working on org.clojure/clojurescript {:mvn/version "1.11.60"}

(ns contrib.cljs-target
  #?(:cljs (:require-macros [contrib.cljs-target]))
  #?(:cljs (:require [goog.object :as object])))

; preferred runtime check for target through public API https://cljs.github.io/api/cljs.core/STARtargetSTAR
#?(:cljs (defn nodejs? [] (= cljs.core/*target* "nodejs")))
#?(:cljs (defn browser? [] (= cljs.core/*target* "default")))

; undocumented hack, only works in macros. https://stackoverflow.com/a/47499855
#?(:clj (defn- cljs-target [] (get-in @cljs.env/*compiler* [:options :closure-defines 'cljs.core/*target*])))

(defmacro do-nodejs  [& body] (if     (= "nodejs" (cljs-target)) `(do ~@body)))
(defmacro do-browser [& body] (if-not (= "nodejs" (cljs-target)) `(do ~@body)))