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+// 1. Try to create a couple of different situation with context (this) losing
+// and fix them with: 
+// - call, apply, bind
+// - arrow functions
+const firstObj = {
+    objHeight: 175,
+    sayHeigth: function () {
+        return this.objHeight + ' good!';
+    }
+};
+//var getH = firstObj.sayHeight;  //undefined (value 'this' have a meaning windows)
+//getH(); //TypeError
+firstObj.sayHeigth.call(firstObj);//175 good! ('call' set value 'this' = firstObj)
+firstObj.sayHeigth.apply(firstObj);//175 good! (also)
+var getH = firstObj.sayHeigth.bind(firstObj); //(to bind context 'this' with func firstObj)
+getH();// 175 good!
+const sayHh = () => firstObj.sayHeigth();//directly set value 'yhis' context 
+sayHh(); //175 good!
+
+//1.2 
+Math.max(3, 6, 1, 8, 2);//8
+var arrFind = [3, 6, 1, 8, 2];
+Math.max(arrFind);//NaN 
+//somewhat we lose this because Math.max leads to number array
+Math.max.apply(Math, arrFind);
+
+//Object example for ex. 2 / 3
+
+const menu = [{
+    product_name: "burger menu",
+    tax: 0.5,
+    subtotal: 4.5,
+    total: 5,
+    items: [
+        {
+            product_name: "french fries",
+            tax: 0,
+            subtotal: 2,
+            total: 2,
+            entity_id: "someId2",
+            parent_id: "someId1",
+            items: [
+                {
+                    product_name: "ketchup",
+                    tax: 0,
+                    subtotal: 1,
+                    total: 1,
+                    entity_id: "someId3",
+                    parent_id: "someId2",
+                }
+            ],
+        },
+    ],
+    entity_id: "someId1",
+}];
+
+// 2. Create nested obects tree structure (3 levels nesting):
+// Implement all posible, that you know, clone methods (including cloning the nested properties)
+// 2.1 Easy cloning 
+// this variants (2,1 - 2.3) is not situable for nested properties
+
+const menu = {
+    product_name: "burger menu",
+    tax: 0.5,
+    subtotal: 4.5,
+    total: 5,
+    items: [
+        {
+            product_name: "french fries",
+            tax: 0,
+            subtotal: 2,
+            total: 2,
+            entity_id: "someId2",
+            parent_id: "someId1",
+            items: [
+                {
+                    product_name: "ketchup",
+                    tax: 0,
+                    subtotal: 1,
+                    total: 1,
+                    entity_id: "someId3",
+                    parent_id: "someId2",
+                }
+            ],
+        },
+    ],
+    entity_id: "someId1",
+}
+
+function copy(mainObj) {
+    let objCopy = {}; // objCopy will store mainObj
+    let key;
+
+    for (key in mainObj) {
+        objCopy[key] = mainObj[key]; // copy all properties into objCopy
+    }
+    return objCopy;
+}
+console.log(copy(menu));
+//0: {product_name: "burger menu", tax: 0.5, subtotal: 4.5, total: 5, items: Array(1), …}
+
+
+// 2.2 Spread {... obj}
+var cloneMenu1 = { ...menu };
+console.log(cloneMenu1);
+//0: {product_name: "burger menu", tax: 0.5, subtotal: 4.5, total: 5, items: Array(1), …}
+
+
+//2.3 Object.assign({}, obj)
+const cloneMenu2 = Object.assign({}, menu);
+console.log(cloneMenu2);
+//0: {product_name: "burger menu", tax: 0.5, subtotal: 4.5, total: 5, items: Array(1), …}
+
+//2.4 JSON cloning
+const cloneMenuJSON = JSON.parse(JSON.stringify(menu))//qwikly but
+//JSON cannot contain functions. This means that not every object can be cloned without loss.
+console.log(cloneMenuJSON);
+
+
+// 3. Create tree of nested objects
+// Use objects structure from example 2, generate flat Map set (key-value), here will be 
+//stored spesific user information.
+// for example(you created products collection with nested products inside),
+// by unic product id create list of product_id-product price.
+const menu3 = [{
+    product_name: "burger menu3",
+    tax: 0.5,
+    subtotal: 4.5,
+    total: 5,
+    id: "someId1",
+    items: [{
+        product_name: "french fries",
+        tax: 0,
+        subtotal: 2,
+        total: 2,
+        id: "someId2",
+        items: [{
+            product_name: "ketchup",
+            tax: 0,
+            subtotal: 1,
+            total: 1,
+            id: "someId3"
+        }, {
+            product_name: "ketchup_two",
+            tax: 0,
+            subtotal: 1,
+            total: 1,
+            id: "someId3"
+        }, {
+            product_name: "ketchup",
+            tax: 0,
+            subtotal: 1,
+            total: 1,
+            id: "someId4"
+        }, {
+            product_name: "ketchup_three",
+            tax: 0,
+            subtotal: 1,
+            total: 1,
+            id: "someId3"
+        }]
+    }]
+}];
+
+var menuItems = new Map();
+
+getMapNoDublicate(menu3);
+
+function getMapNoDublicate(data) {
+    for (let i = 0; i < data.length; i++) {
+        menuItems.set(data[i].id, data[i]);//method map.set() - add object if it does not exist (OR)
+        //                                                    - if it exist then updates element and i can use it like a checking
+
+        if (data[i].items) {
+            getMapNoDublicate(data[i].items);
+        }
+    }
+
+    return data;
+}
+
+console.log(menuItems.keys());
+console.log(menuItems.values());