My Solution

spec/MyArraySpec.js

@@ -57,12 +57,16 @@ describe('MyArray', function () {
             array.push('1');
             array.push(3);
             array.push('hello');
+            array.push('hello');
+            array.push('hello');
 
-            expect(array.length()).toEqual(4);
+            expect(array.length()).toEqual(6);
             expect(array.get(0)).toEqual(42);
             expect(array.get(1)).toEqual('1');
             expect(array.get(2)).toEqual(3);
             expect(array.get(3)).toEqual('hello');
+            expect(array.get(4)).toEqual('hello');
+            expect(array.get(5)).toEqual('hello');
         });
     });
 
@@ -203,7 +207,7 @@ describe('MyArray', function () {
         it('returns index of the only occurrence', function () {
             var array = MyArray.of(1, '2', 2, 4);
 
-            expect(array.indexOf(2)).toEqual(2);
+            expect(array.indexOf(4)).toEqual(3);
         });
 
         it('returns index of the first occurrence', function () {

src/MyArray.js

@@ -8,105 +8,281 @@ function MyArray(initialCapacity) {
 }
 
 MyArray.prototype.length = function () {
+    return this.size;
+};
 
+MyArray.prototype.resize = function (newCapacity) {
+    var biggerArr = new PlainArray(newCapacity);
+    for (var i = 0; i < this.size; i++) {
+        biggerArr.set(i, this.elements.get(i));
+    }
+    this.elements = biggerArr;
 };
 
 MyArray.prototype.push = function (value) {
 
+    if (this.elements.length === this.size) {
+        this.resize(this.elements.length + 1);
+    }
+
+    this.elements.set(this.size, value);
+    this.size++;
 };
 
 MyArray.prototype.get = function (index) {
-
+    if (index < this.size && index >= 0) {
+        return this.elements.get(index);
+    }
+    return undefined;
 };
 
 MyArray.prototype.set = function (index, value) {
 
+    if (this.elements.length <= index) {
+        this.resize(index + 1);
+    }
+
+    if (index >= this.size) {
+        this.size = index + 1;
+    }
+    return this.elements.set(index, value);
 };
 
 MyArray.of = function () {
-
+    var array = new MyArray();
+    for (var i = 0; i < arguments.length; i++) {
+        array.push(arguments[i]);
+    }
+    return array;
 };
 
 MyArray.prototype.pop = function () {
+    if (this.size <= 0) {
+        return undefined;
+    }
 
+    var value = this.get(this.size - 1);
+    this.size--;
+    return value;
 };
 
 MyArray.prototype.concat = function (other) {
+    var newArr = new MyArray(this.size + other.size);
+    for (var i = 0; i < this.size; i++) {
+        var getItem = this.get(i);
+        newArr.set(i, getItem);
+    }
 
+    for (var j = 0; j < other.size; j++) {
+        var getItemOfOther = other.get(j);
+        newArr.set(this.size + j, getItemOfOther);
+    }
+    return newArr;
 };
 
 MyArray.prototype.indexOf = function (element) {
+    for (var i = 0; i < this.size; i++) {
+        if (this.get(i) === element) {
+            return i;
+        }
+    }
 
+    return -1;
 };
 
 MyArray.prototype.lastIndexOf = function (element) {
-
+    for (var i = this.size - 1; i >= 0; i--) {
+        if (this.get(i) === element) {
+            return i;
+        }
+    }
+    return -1;
 };
 
 MyArray.prototype.includes = function (element) {
-
+    for (var i = 0; i < this.size; i++) {
+        if (this.get(i) === element) {
+            return true;
+        }
+    }
+    return false;
 };
 
 MyArray.prototype.find = function (fn) {
+    var element;
+    for (var i = 0; i < this.size; i++) {
+        element = this.get(i);
+        if (fn(element)) {
+            return element;
+        }
+    }
 
 };
 
 MyArray.prototype.findIndex = function (fn) {
-
+    var element;
+    for (var i = 0; i < this.size; i++) {
+        element = this.get(i);
+        if (fn(element)) {
+            return i;
+        }
+    }
+    return -1;
 };
 
 MyArray.prototype.equals = function (other) {
 
+    if (this.size !== other.size) {
+        return false;
+    }
+
+    // Object.is(value1, value2)
+    for (var i = 0; i < this.size; i++) {
+        if (this.get(i) !== other.get(i)) {
+            return false;
+        }
+    }
+    return true;
 };
 
 MyArray.prototype.forEach = function (fn) {
-
+    var element;
+    for (var i = 0; i < this.size; i++) {
+        element = this.get(i);
+        // currentValue, index
+        fn(element, i);
+    }
 };
 
 MyArray.prototype.join = function (separator) {
+    if (separator === undefined) {
+        separator = ',';
+    }
+    var result = '';
+
+    for (var i = 0; i < this.size; i++) {
+        result += this.get(i);
 
+        if (i < this.size - 1) {
+            result += separator;
+        }
+    }
+    return result;
 };
 
 MyArray.prototype.toString = function () {
-
+    return this.join();
 };
 
 MyArray.prototype.map = function (fn) {
+    var newArr = new MyArray(this.size);
 
+    this.forEach(function (element, i) {
+        newArr.set(i, fn(element, i));
+    });
+    return newArr;
 };
 
 MyArray.prototype.filter = function (fn) {
-
+    var newArr = new MyArray(this.size);
+
+    this.forEach(function (element, i) {
+        if (fn(element, i)) {
+            newArr.push(element);
+        }
+    });
+    return newArr;
 };
 
 MyArray.prototype.some = function (fn) {
-
+    return this.find(fn) !== undefined;
 };
 
 MyArray.prototype.every = function (fn) {
-
+    return this.filter(fn).length() === this.size;
 };
 
 MyArray.prototype.fill = function (value, start, end) {
 
+    if (start === undefined) {
+        start = 0;
+    }
+
+    if (end === undefined) {
+        end = this.size;
+    }
+
+    for (var i = start; i < end; i++) {
+        this.set(i, value);
+    }
 };
 
 MyArray.prototype.reverse = function () {
+    for (var i = 0; i < this.size / 2; i++) {
+        var a = this.get(i);
+        var b = this.get(this.size - i - 1);
 
+        this.set(i, b);
+        this.set(this.size - i - 1, a);
+    }
 };
 
 MyArray.prototype.shift = function () {
 
+    if (this.size === 0) {
+        return undefined;
+    }
+
+    var element = this.get(0);
+    for (var i = 0; i < this.size; i++) {
+        this.set(i, this.get(i + 1));
+    }
+    this.size--;
+    return element;
 };
 
 MyArray.prototype.unshift = function (element) {
-
+    for (var i = this.size; i > 0; i--) {
+        this.set(i, this.get(i - 1));
+    }
+    this.set(0, element);
 };
 
 MyArray.prototype.slice = function (start, end) {
+    if (start === undefined) {
+        start = 0;
+    }
+
+    if (end === undefined) {
+        end = this.size;
+    }
 
+    var newArr = new MyArray(this.size);
+
+    for (var i = start; i < end; i++) {
+        newArr.set(i - start, this.get(i));
+    }
+    return newArr;
 };
 
 MyArray.prototype.splice = function (start, deleteCount) {
 
+    if (deleteCount === undefined) {
+        deleteCount = this.size - start;
+    }
+
+    var prefix = this.slice(0, start);
+
+    var middle = new MyArray();
+
+    for (var i = 2; i < arguments.length; i++) {
+        middle.push(arguments[i]);
+    }
+
+    var suffix = this.slice(start + deleteCount);
+
+    var newArr = prefix.concat(middle).concat(suffix);
+
+    this.elements = newArr.elements;
+    this.size = newArr.size;
 };