diff --git a/playground/update.sh b/playground/update.sh
index 188aeb8d..5d62c702 100755
--- a/playground/update.sh
+++ b/playground/update.sh
@@ -1,6 +1,15 @@
 #!/bin/sh
 set -e
 
+tmp=$(mktemp -d "${TMPDIR:-/tmp}/gopherjs_playground.XXXXXXXXXX")
+
+cleanup() {
+    rm -rf "$tmp"
+    exit
+}
+
+trap cleanup EXIT SIGHUP SIGINT SIGTERM
+
 go install github.com/gopherjs/gopherjs/...
 
 go generate github.com/gopherjs/gopherjs.github.io/playground/internal/imports
@@ -9,31 +18,126 @@ go generate github.com/gopherjs/gopherjs.github.io/playground/internal/imports
 gopherjs build -m
 
 # The GOPATH workspace where the GopherJS project is.
-GOPHERJSGOPATH=$(go list -f '{{.Root}}' github.com/gopherjs/gopherjs)
+gopherjsgopath=$(go list -f '{{.Root}}' github.com/gopherjs/gopherjs)
 
-PKG=pkg
-rm -r $PKG
+rm -r pkg/
 
 # Use an empty GOPATH workspace with just gopherjs,
 # so that all the standard library packages get written to GOROOT/pkg.
-export GOPATH=/tmp/gopherjsplayground_gopath
-mkdir -p $GOPATH/src/github.com/gopherjs/gopherjs
-cp -r $GOPHERJSGOPATH/src/github.com/gopherjs/gopherjs/* $GOPATH/src/github.com/gopherjs/gopherjs
+export GOPATH="$tmp/gopath"
+mkdir -p "$GOPATH"/src/github.com/gopherjs/gopherjs
+cp -a "$gopherjsgopath"/src/github.com/gopherjs/gopherjs/* "$GOPATH"/src/github.com/gopherjs/gopherjs
 
 gopherjs install -m github.com/gopherjs/gopherjs/js github.com/gopherjs/gopherjs/nosync
-mkdir -p $PKG/github.com/gopherjs/gopherjs
-cp $GOPATH/pkg/darwin_js_min/github.com/gopherjs/gopherjs/js.a $PKG/github.com/gopherjs/gopherjs/js.a
-cp $GOPATH/pkg/darwin_js_min/github.com/gopherjs/gopherjs/nosync.a $PKG/github.com/gopherjs/gopherjs/nosync.a
+mkdir -p pkg/github.com/gopherjs/gopherjs
+cp "$GOPATH"/pkg/*_js_min/github.com/gopherjs/gopherjs/js.a pkg/github.com/gopherjs/gopherjs/js.a
+cp "$GOPATH"/pkg/*_js_min/github.com/gopherjs/gopherjs/nosync.a pkg/github.com/gopherjs/gopherjs/nosync.a
 
 # Make a copy of GOROOT that is user-writeable,
 # use it to build and copy out standard library packages.
-cp -r $(go env GOROOT) /tmp/gopherjsplayground_goroot
-export GOROOT=/tmp/gopherjsplayground_goroot
-gopherjs install -m archive/tar archive/zip bufio bytes compress/bzip2 compress/flate compress/gzip compress/lzw compress/zlib container/heap container/list container/ring crypto/aes crypto/cipher crypto/des crypto/dsa crypto/ecdsa crypto/elliptic crypto/hmac crypto/md5 crypto/rand crypto/rc4 crypto/rsa crypto/sha1 crypto/sha256 crypto/sha512 crypto/subtle database/sql/driver debug/gosym debug/pe encoding/ascii85 encoding/asn1 encoding/base32 encoding/base64 encoding/binary encoding/csv encoding/gob encoding/hex encoding/json encoding/pem encoding/xml errors fmt go/ast go/doc go/format go/printer go/token hash/adler32 hash/crc32 hash/crc64 hash/fnv html html/template image image/color image/draw image/gif image/jpeg image/png index/suffixarray io io/ioutil math math/big math/cmplx math/rand mime net/http/cookiejar net/http/fcgi net/http/httptest net/http/httputil net/mail net/smtp net/textproto net/url path path/filepath reflect regexp regexp/syntax runtime/internal/sys sort strconv strings sync/atomic testing testing/iotest testing/quick text/scanner text/tabwriter text/template text/template/parse time unicode unicode/utf16 unicode/utf8
-cp -r $GOROOT/pkg/darwin_js_min/* $PKG
-cp -r $GOROOT/pkg/darwin_amd64_js_min/* $PKG
+cp -a "$(go env GOROOT)" "$tmp/goroot"
+export GOROOT="$tmp/goroot"
+gopherjs install -m \
+         archive/tar \
+         archive/zip \
+         bufio \
+         bytes \
+         compress/bzip2 \
+         compress/flate \
+         compress/gzip \
+         compress/lzw \
+         compress/zlib \
+         container/heap \
+         container/list \
+         container/ring \
+         crypto/aes \
+         crypto/cipher \
+         crypto/des \
+         crypto/dsa \
+         crypto/ecdsa \
+         crypto/elliptic \
+         crypto/hmac \
+         crypto/md5 \
+         crypto/rand \
+         crypto/rc4 \
+         crypto/rsa \
+         crypto/sha1 \
+         crypto/sha256 \
+         crypto/sha512 \
+         crypto/subtle \
+         database/sql/driver \
+         debug/gosym \
+         debug/pe \
+         encoding/ascii85 \
+         encoding/asn1 \
+         encoding/base32 \
+         encoding/base64 \
+         encoding/binary \
+         encoding/csv \
+         encoding/gob \
+         encoding/hex \
+         encoding/json \
+         encoding/pem \
+         encoding/xml \
+         errors \
+         fmt \
+         go/ast \
+         go/doc \
+         go/format \
+         go/printer \
+         go/token \
+         hash/adler32 \
+         hash/crc32 \
+         hash/crc64 \
+         hash/fnv \
+         html \
+         html/template \
+         image \
+         image/color \
+         image/draw \
+         image/gif \
+         image/jpeg \
+         image/png \
+         index/suffixarray \
+         io \
+         io/ioutil \
+         math \
+         math/big \
+         math/cmplx \
+         math/rand \
+         mime \
+         net/http/cookiejar \
+         net/http/fcgi \
+         net/http/httptest \
+         net/http/httputil \
+         net/mail \
+         net/smtp \
+         net/textproto \
+         net/url \
+         path \
+         path/filepath \
+         reflect \
+         regexp \
+         regexp/syntax \
+         runtime/internal/sys \
+         sort \
+         strconv \
+         strings \
+         sync/atomic \
+         testing \
+         testing/iotest \
+         testing/quick \
+         text/scanner \
+         text/tabwriter \
+         text/template \
+         text/template/parse \
+         time \
+         unicode \
+         unicode/utf16 \
+         unicode/utf8
 
-rm -r /tmp/gopherjsplayground_goroot
-rm -r /tmp/gopherjsplayground_gopath
+cp -a "$GOROOT"/pkg/*_js_min/* pkg/
+cp -a "$GOROOT"/pkg/*_amd64_js_min/* pkg/
 
-rename 's/\.a/\.a.js/' $(find $PKG -name "*.a")
+# Rename all *.a files in pkg/ to *.a.js.
+find pkg -name "*.a" -exec sh -c 'mv $0 $0.js' {} \;