diff --git a/README.md b/README.md
index 3f91b3a..e773a60 100644
--- a/README.md
+++ b/README.md
@@ -15,14 +15,17 @@ usage
 ```js
 var sortJson = require('sort-json');
 
-var copy = sortJson(object);
+var copy = sortJson(object, key);
+and if there is no key 
+var copy = sortJson(object, null);
 ```
 
 CLI usage
 ---------
 `sort-json file.json`
-
-For now sort-json takes no other arguments, so the original file will be overwritten by a sorted JSON file, keeping the indentation of the original file.
+or if you want to sort by key ("id" for example):
+`sort-json file.json -k id` or `sort-json file.json --key id`
+The original file will be overwritten by a sorted JSON file, keeping the indentation of the original file.
 
 tests
 -----
diff --git a/cmd.js b/cmd.js
index 7a02bd7..06650a2 100755
--- a/cmd.js
+++ b/cmd.js
@@ -9,7 +9,22 @@ var detectIndent = require('detect-indent');
 var sortJson = require('./');
 
 // Get all the files
-var files = process.argv.slice(2);
+var files = process.argv.splice(2, 3);
+var key = null;
+
+for (var x = 0; x < files.length; x++){
+  if (files[x] === "-k" || files[x] === '--key'){
+    if (files.length !== x + 2){
+      console.log("error: no key was given, ignoring the flag");
+      files.pop();
+      break;
+    } else {
+      key = files.pop();
+      files.pop();
+      break;
+    }
+  }
+}
 
 files.forEach(readEachFile);
 
@@ -37,7 +52,7 @@ function readEachFile(fileName) {
     }
 
     // Sorting
-    var sortedObject = sortJson(json);
+    var sortedObject = sortJson(json, key);
 
     // Saving to file
     fs.writeFile(filePath, JSON.stringify(sortedObject, null, indent) + ((eol && eol.length === 2) ? eol[1] : ''), function(err) {
diff --git a/index.js b/index.js
index 0bd007d..e5321a9 100644
--- a/index.js
+++ b/index.js
@@ -1,13 +1,22 @@
 module.exports = visit;
 
-function visit(old) {
+function visit(old, mainKey) {
     if (typeof(old) !== 'object' || old === null) {
         return old;
     }
     var copy = Array.isArray(old) ? [] : {};
-    var keys = Object.keys(old).sort();
-    keys.forEach(function(key) {
-        copy[key] = visit(old[key]);
-    });
+    if (mainKey === null){
+    	var keys = Object.keys(old).sort();
+        keys.forEach(function(key) {
+            copy[key] = visit(old[key], null);
+        });
+    } else {
+    	for (var x = 0; x < old.length; x++){
+    		old.sort(function(a, b){
+                return (a[mainKey] - b[mainKey])
+    		});
+    	}
+    	return (old);
+    }
     return copy;
 }
diff --git a/package-lock.json b/package-lock.json
new file mode 100644
index 0000000..5d615e4
--- /dev/null
+++ b/package-lock.json
@@ -0,0 +1,37 @@
+{
+  "name": "sort-json",
+  "version": "1.4.1",
+  "lockfileVersion": 1,
+  "requires": true,
+  "dependencies": {
+    "detect-indent": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/detect-indent/-/detect-indent-4.0.0.tgz",
+      "integrity": "sha1-920GQ1LN9Docts5hnE7jqUdd4gg=",
+      "requires": {
+        "repeating": "2.0.1"
+      }
+    },
+    "is-finite": {
+      "version": "1.0.2",
+      "resolved": "https://registry.npmjs.org/is-finite/-/is-finite-1.0.2.tgz",
+      "integrity": "sha1-zGZ3aVYCvlUO8R6LSqYwU0K20Ko=",
+      "requires": {
+        "number-is-nan": "1.0.1"
+      }
+    },
+    "number-is-nan": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/number-is-nan/-/number-is-nan-1.0.1.tgz",
+      "integrity": "sha1-CXtgK1NCKlIsGvuHkDGDNpQaAR0="
+    },
+    "repeating": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/repeating/-/repeating-2.0.1.tgz",
+      "integrity": "sha1-UhTFOpJtNVJwdSf7q0FdvAjQbdo=",
+      "requires": {
+        "is-finite": "1.0.2"
+      }
+    }
+  }
+}
diff --git a/package.json b/package.json
index c55030f..054dd28 100644
--- a/package.json
+++ b/package.json
@@ -27,7 +27,7 @@
     "type": "git",
     "url": "https://github.com/kesla/sort-json.git"
   },
-  "author": "David Björklund <david.bjorklund@gmail.com>",
+  "authors": "David Björklund <david.bjorklund@gmail.com>, Nathan Schwarz <nathan.schwarz97@gmail.com>",
   "license": "MIT",
   "bugs": {
     "url": "https://github.com/kesla/sort-json/issues"