stream: refactor getHighWaterMark in state.js

This commit aims to reduce some code duplication in state.js

PR-URL: #20415
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/internal/streams/state.js

@@ -2,19 +2,19 @@
 
 const { ERR_INVALID_OPT_VALUE } = require('internal/errors').codes;
 
+function highWaterMarkFrom(options, isDuplex, duplexKey) {
+  return options.highWaterMark != null ? options.highWaterMark :
+    isDuplex ? options[duplexKey] : null;
+}
+
 function getHighWaterMark(state, options, duplexKey, isDuplex) {
-  let hwm = options.highWaterMark;
+  const hwm = highWaterMarkFrom(options, isDuplex, duplexKey);
   if (hwm != null) {
-    if (typeof hwm !== 'number' || !(hwm >= 0))
-      throw new ERR_INVALID_OPT_VALUE('highWaterMark', hwm);
-    return Math.floor(hwm);
-  } else if (isDuplex) {
-    hwm = options[duplexKey];
-    if (hwm != null) {
-      if (typeof hwm !== 'number' || !(hwm >= 0))
-        throw new ERR_INVALID_OPT_VALUE(duplexKey, hwm);
-      return Math.floor(hwm);
+    if (!Number.isInteger(hwm) || hwm < 0) {
+      const name = isDuplex ? duplexKey : 'highWaterMark';
+      throw new ERR_INVALID_OPT_VALUE(name, hwm);
     }
+    return Math.floor(hwm);
   }
 
   // Default value