uv: improvements to process.binding('uv')

* ensure that UV_... props are constants
* improve error message ... the error message when passing
  in `err >= 0` to `util._errnoException()` was less than
   useful.
* refine uses of process.binding('uv')

PR-URL: https://github.com/nodejs/node/pull/14933
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

1 files changed, 6 insertions, 8 deletions

diff --git a/lib/_stream_wrap.js b/lib/_stream_wrap.js
index 00e6de2fd2..5ae091614f 100644
--- a/lib/_stream_wrap.js
+++ b/lib/_stream_wrap.js
@@ -129,20 +129,18 @@ StreamWrap.prototype.doWrite = function doWrite(req, bufs) {
     // Ensure that this is called once in case of error
     pending = 0;
 
+    let errCode = 0;
+    if (err) {
+      const code = uv[`UV_${err.code}`];
+      errCode = (err.code && code) ? code : uv.UV_EPIPE;
+    }
+
     // Ensure that write was dispatched
     setImmediate(function() {
       // Do not invoke callback twice
       if (!self._dequeue(item))
         return;
 
-      var errCode = 0;
-      if (err) {
-        if (err.code && uv['UV_' + err.code])
-          errCode = uv['UV_' + err.code];
-        else
-          errCode = uv.UV_EPIPE;
-      }
-
       handle.doAfterWrite(req);
       handle.finishWrite(req, errCode);
     });