better async js support

buildroot-v86/board/v86/rootfs_overlay/bin/js

@@ -19,13 +19,20 @@ test -f "$1" && {
 
 OUTPUT=/mnt/run/$PID # com/isoterminal/feat/javascript.js writes output here
 
-touch $OUTPUT
 echo -n "PID=$PID; $javascript" > /dev/browser/js
-# todo watch file 
-sleep 0.1
-cat $OUTPUT 
-rm $OUTPUT
 
+# check for file output
+check_ready(){ 
+  test -f $OUTPUT && { 
+    cat $OUTPUT | grep -vE '^undefined$'; 
+    code="$(cat ${OUTPUT}.exit)"
+    rm $OUTPUT; 
+    exit $code;  
+  }
+}
+
+check_ready
+while sleep 0.3; do check_ready; done 
 
 # should we use flock, an awesome way to make processes read/write the same file
 # while preventing 1001 concurrency issues?

buildroot-v86/board/v86/rootfs_overlay/root/manual.md

@@ -251,3 +251,16 @@ Various options:
 3. Run `jsh alert hello` in the shell
 4. Run `jsh` to start an interactive shell
 
+This allow writing (a)synchronous cli-scripts which execute in the browser:
+
+```
+#!/bin/js
+return "hello"
+```
+
+```
+#!/bin/js
+return new Promise( (resolve,reject) => resolve("hello") )
+```
+
+NOTE: For convenience the javascript-code is passed to browser-context (via the webworker). In the future a package like [quickjs](https://bellard.org/quickjs/) will isolate things further.