--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -250,16 +250,17 @@ def wanted_mozconfig_variables(help):
          'AUTOCONF',
          'AWK',
          'DISABLE_EXPORT_JS',
          'DISABLE_SHARED_JS',
          'DOXYGEN',
          'DSYMUTIL',
          'EXTERNAL_SOURCE_DIR',
          'GENISOIMAGE',
+         'JS_STANDALONE',
          'L10NBASEDIR',
          'MOZILLABUILD',
          'MOZ_ARTIFACT_BUILDS',
          'MOZ_BUILD_APP',
          'MOZ_CALLGRIND',
          'MOZ_DMD',
          'MOZ_FMP4',
          'MOZ_INSTRUMENT_EVENT_LOOP',

--- a/js/moz.configure
+++ b/js/moz.configure
@@ -3,38 +3,48 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 # /!\ Use js_option() instead of option() in this file. /!\
 # =========================================================
 
 @depends(build_project, '--help')
-def js_shell_default(build_project, help):
+def building_js(build_project, help):
     return build_project == 'js'
 
-js_option('--disable-js-shell', default=js_shell_default,
+# Exception to the rule above: JS_STANDALONE is a special option that doesn't
+# want the js_option treatment. When we're done merging js/src/configure and
+# top-level configure, it can go away, although the JS_STANDALONE config
+# will still need to be set depending on building_js above.
+option(env='JS_STANDALONE', default=building_js,
+       help='Reserved for internal use')
+
+@depends('JS_STANDALONE')
+def js_standalone(value):
+    if value:
+        set_config('JS_STANDALONE', '1')
+        add_old_configure_assignment('JS_STANDALONE', '1')
+
+
+js_option('--disable-js-shell', default=building_js,
        help='Do not build the JS shell')
 
 @depends('--disable-js-shell')
 def js_shell(value):
     if not value:
         set_config('JS_DISABLE_SHELL', '1')
 
 
 # SpiderMonkey as a shared library, and how its symbols are exported
 # ==================================================================
-@depends(build_project, '--help')
-def js_shared_default(build_project, help):
-    return build_project == 'js'
-
-js_option('--disable-shared-js', default=js_shared_default,
+js_option('--disable-shared-js', default=building_js,
           help='Do not create a shared library')
 
-js_option('--disable-export-js', default=js_shared_default,
+js_option('--disable-export-js', default=building_js,
           help='Do not mark JS symbols as DLL exported/visible')
 
 @depends('--disable-shared-js', '--disable-export-js')
 def static_js(shared_js, export_js):
     if shared_js:
         if not export_js:
             error('Must export JS symbols when building a shared library.')
         set_config('JS_SHARED_LIBRARY', '1')

--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -70,26 +70,22 @@ dnl Do not allow objdir == srcdir builds
 dnl ==============================================================
 _topsrcdir=`cd $srcdir; pwd -W 2>/dev/null || pwd -P`
 _objdir=`pwd -P`
 
 MOZ_BUILD_ROOT=`pwd -W 2>/dev/null || pwd -P`
 
 MOZ_DEFAULT_COMPILER
 
-if test "$JS_STANDALONE" = no; then
+if test -z "$JS_STANDALONE"; then
   autoconfmk=autoconf-js.mk
-  JS_STANDALONE=
   #DIST is exported from top-level configure
 else
-  JS_STANDALONE=1
-  AC_DEFINE(JS_STANDALONE)
   DIST="$MOZ_BUILD_ROOT/dist"
 fi
-AC_SUBST(JS_STANDALONE)
 AC_SUBST(autoconfmk)
 
 MOZ_ARG_WITH_STRING(gonk-toolchain-prefix,
 [  --with-gonk-toolchain-prefix=DIR
                           prefix to gonk toolchain commands],
     gonk_toolchain_prefix=$withval)
 
 if test -n "$gonkdir" ; then

--- a/old-configure.in
+++ b/old-configure.in
@@ -7934,17 +7934,17 @@ export MOZ_SYSTEM_ZLIB
 export MOZ_ZLIB_CFLAGS
 export MOZ_ZLIB_LIBS
 export MOZ_APP_NAME
 export MOZ_APP_REMOTINGNAME
 export RUSTC
 export MOZILLA_CENTRAL_PATH=$_topsrcdir
 export STLPORT_CPPFLAGS
 export STLPORT_LIBS
-export JS_STANDALONE=no
+export JS_STANDALONE=
 export DIST
 export MOZ_LINKER
 export ZLIB_IN_MOZGLUE
 export MOZ_MEMORY
 export AR
 export RANLIB
 export CPP
 export CC