add array head and tail helper

lib/array.js

@@ -11,6 +11,20 @@ module.exports = {
 
     ensureArray: val => Array.isArray(val) ? val : [val],
 
+    head (ar) {
+        checkArray(ar);
+
+        const [head, ...rest] = ar;
+        return head;
+    },
+
+    tail (ar) {
+        checkArray(ar);
+
+        const [ tail ] = ar.slice(-1);
+        return tail;
+    },
+
     unique (ar) {
         checkArray(ar);
         return ar.filter((val, i, input) => i === input.indexOf(val));

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@mightyplow/jslib",
-  "version": "0.5.1",
+  "version": "0.6.0",
   "description": "js, helpers library",
   "main": "jslib.js",
   "devDependencies": {