avoid process.binding() where possible (#5)

avoid process.binding() where possible

process.binding() is deprecated. When running recent versions of Node.js
with --pending-deprecation, the current code results in a printed
warning about process.binding() usage. process.binding() is used to
create writev(), but Node.js now exposes fs.writev(). Use that instead
when it exists. Otherwise, fall back to the polyfill. This will avoid
runtime deprecation messages for end users.

If the minimum supported engine is ever Node.js 12.9.0 or above, the
polyfill code should be removable at that time.

index.js

@@ -3,11 +3,21 @@ const MiniPass = require('minipass')
 const EE = require('events').EventEmitter
 const fs = require('fs')
 
-// for writev
-const binding = process.binding('fs')
-const writeBuffers = binding.writeBuffers
+let writev = fs.writev
 /* istanbul ignore next */
-const FSReqWrap = binding.FSReqWrap || binding.FSReqCallback
+if (!writev) {
+  // This entire block can be removed if support for earlier than Node.js
+  // 12.9.0 is not needed.
+  const binding = process.binding('fs')
+  const FSReqWrap = binding.FSReqWrap || binding.FSReqCallback
+
+  writev = (fd, iovec, pos, cb) => {
+    const done = (er, bw) => cb(er, bw, iovec)
+    const req = new FSReqWrap()
+    req.oncomplete = done
+    binding.writeBuffers(fd, iovec, pos, req)
+  }
+}
 
 const _autoClose = Symbol('_autoClose')
 const _close = Symbol('_close')
@@ -373,13 +383,6 @@ class WriteStreamSync extends WriteStream {
   }
 }
 
-const writev = (fd, iovec, pos, cb) => {
-  const done = (er, bw) => cb(er, bw, iovec)
-  const req = new FSReqWrap()
-  req.oncomplete = done
-  binding.writeBuffers(fd, iovec, pos, req)
-}
-
 exports.ReadStream = ReadStream
 exports.ReadStreamSync = ReadStreamSync