Merge pull request #73 from uncaughtxcptn/feature/eachIndex-method

Feature/.eachIndex() method

index.js

@@ -19,6 +19,7 @@ import dig from './methods/dig';
 import drop from './methods/drop';
 import dropWhile from './methods/dropWhile';
 import each from './methods/each';
+import eachIndex from './methods/eachIndex';
 
 const handlers = {
     all,
@@ -41,7 +42,8 @@ const handlers = {
     dig,
     drop,
     dropWhile,
-    each
+    each,
+    eachIndex
 };
 
 export default function rbjs(toProxy) {

methods/eachIndex/index.js

@@ -0,0 +1,24 @@
+/**
+ *  Iterates the items of the array and passes their index to the callback.
+ *
+ *  @param {Array} array
+ *  @param {Function} callback - The function that will be passed the indeces
+ *      of each array item.
+ *
+ *  @return {Array} The original given array.
+ *
+ *  @example
+ *  eachIndex(['a', 'b', 'c'], i => console.log(i)); // prints: 0 1 2
+ *
+ *  @example
+ *  rbjs(['a', 'b', 'c']).eachIndex(i => console.log(i)); // prints: 0 1 2
+ */
+export default function eachIndex(array, callback) {
+    if (typeof callback !== 'function') {
+        throw new TypeError('Parameter "callback" must be a function.');
+    }
+
+    array.forEach((item, i) => callback(i));
+
+    return array;
+}

methods/eachIndex/tests.js

@@ -0,0 +1,27 @@
+import test from 'ava';
+import eachIndex from '.';
+
+test('passes the index of each item to the callback', t => {
+    const results = [];
+    const callback = x => results.push(x);
+
+    eachIndex([1, 2, 3, 4, 5], callback);
+
+    t.deepEqual(results, [0, 1, 2, 3, 4]);
+});
+
+test('returns the given array', t => {
+    const results = [];
+    const callback = x => results.push(x);
+
+    const array = [1, 2, 3, 4, 5];
+
+    t.is(array, eachIndex(array, callback));
+});
+
+test('throws TypeError if callback is not provided', t => {
+    const error = t.throws(() => {
+        eachIndex([1, 2, 3, 4, 5]);
+    }, TypeError);
+    t.is(error.message, 'Parameter "callback" must be a function.');
+});