buffer: refactor to remove some duplicated code in fromObject.

lib/buffer.js

@@ -134,41 +134,36 @@ function fromObject(obj) {
     return b;
   }
 
-  if (Array.isArray(obj)) {
+  if (obj == null) {
+    throw new TypeError('Must start with number, buffer, array or string');
+  }
+
+  function fromArrayLike(obj) {
     const length = obj.length;
     const b = allocate(length);
     for (let i = 0; i < length; i++)
       b[i] = obj[i] & 255;
     return b;
   }
 
-  if (obj == null) {
-    throw new TypeError('Must start with number, buffer, array or string');
+  if (Array.isArray(obj)) {
+    return fromArrayLike(obj);
   }
 
   if (obj instanceof ArrayBuffer) {
     return binding.createFromArrayBuffer(obj);
   }
 
   if (obj.buffer instanceof ArrayBuffer || obj.length) {
-    let length;
-    if (typeof obj.length !== 'number' || obj.length !== obj.length)
-      length = 0;
-    else
-      length = obj.length;
-    const b = allocate(length);
-    for (let i = 0; i < length; i++) {
-      b[i] = obj[i] & 255;
+    if (typeof obj.length !== 'number' || obj.length !== obj.length) {
+      return allocate(0);
+    } else {
+      return fromArrayLike(obj);
     }
-    return b;
   }
 
   if (obj.type === 'Buffer' && Array.isArray(obj.data)) {
-    var array = obj.data;
-    const b = allocate(array.length);
-    for (let i = 0; i < array.length; i++)
-      b[i] = array[i] & 255;
-    return b;
+    return fromArrayLike(obj.data);
   }
 
   throw new TypeError('Must start with number, buffer, array or string');