buffer: refactor to remove some duplicated code in fromObject.

lib/buffer.js

@@ -122,6 +122,13 @@ function fromString(string, encoding) {
   return b;
 }
 
+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;
+}
 
 function fromObject(obj) {
   if (obj instanceof Buffer) {
@@ -135,40 +142,28 @@ function fromObject(obj) {
   }
 
   if (Array.isArray(obj)) {
-    const length = obj.length;
-    const b = allocate(length);
-    for (let i = 0; i < length; i++)
-      b[i] = obj[i] & 255;
-    return b;
+    return fromArrayLike(obj);
   }
 
   if (obj == null) {
     throw new TypeError('Must start with number, buffer, array or string');
   }
 
+
   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');