feat(#20): Implement Array.prototype.flatMap()

Author: giordanna

implementations/flatMap.js

@@ -0,0 +1,42 @@
+/**
+ *
+  MDN Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flatMap
+
+  The flatMap() method first maps each element using a mapping function,
+  then flattens the result into a new array.
+  The flat function is of depth 1.
+
+  The callback function is invoked with three arguments:
+  - currentValue: current element being processed in the array
+  - index: index of the current element being processed
+  - array: array object that was called upon
+
+  thisArg is a value to use as 'this' when executing callback function
+
+  Example 1:
+  [1, 2, 3, 4].flatMap(x => [x, x * 2]);
+  must return:
+  [1, 2, 2, 4, 3, 6, 4, 8]
+
+  Example 2:
+  ["it's Sunny in", "", "California"].flatMap(x => x.split(" "));
+  must return:
+  ["it's","Sunny","in", "", "California"]
+*/
+
+Array.prototype.flatMap = function myFlatMap(callback, thisArg) {
+  const returnValue = [];
+
+  for (let i = 0; i < this.length; i += 1) {
+    const element = callback.call(thisArg, this[i], i, this);
+
+    if (Object.prototype.toString.call(element) === '[object Array]') {
+      for (let j = 0; j < element.length; j += 1) {
+        returnValue.push(element[j]);
+      }
+    } else {
+      returnValue.push(element);
+    }
+  }
+  return returnValue;
+};