feat: add new content objects

Objects chapter added to curriculum

courses/javascript/objects.md

@@ -0,0 +1,276 @@
+---
+title: "Introduction To Javascript"
+subheading: "Objects"
+next: "prototypes"
+prev: "comparisons"
+contentOnly: false
+testCase: [
+			{
+				id: 1,
+				case: ["let user = {};", "let user = {}"],
+				hint: "Defining the object user",
+				isCorrect: false
+			},
+			{
+				id: 2,
+				case: [
+					`user.name = 'Lionel'`,
+					`user.name = 'Lionel';`,
+					`user.name = "Lionel"`,
+					`user.name = "Lionel";`,
+					`user['name'] = 'Lionel'`,
+					`user['name'] = 'Lionel';`,
+					`user['name'] = "Lionel"`,
+					`user['name'] = "Lionel";`,
+					`user["name"] = 'Lionel'`,
+					`user["name"] = 'Lionel';`,
+					`user["name"] = "Lionel"`,
+					`user["name"] = "Lionel";`,
+				],
+				hint: 'Add property "name" with value "Lionel"',
+				isCorrect: false
+			},
+			{
+				id: 3,
+				case: [
+					`user.surName = 'Messi'`,
+					`user.surName = 'Messi';`,
+					`user.surName = "Messi"`,
+					`user.surName = "Messi";`,
+					`user['surName'] = 'Messi'`,
+					`user['surName'] = 'Messi';`,
+					`user['surName'] = "Messi"`,
+					`user['surName'] = "Messi";`,
+					`user["surName"] = 'Messi'`,
+					`user["surName"] = 'Messi';`,
+					`user["surName"] = "Messi"`,
+					`user["surName"] = "Messi";`,
+				],
+				hint: 'Add property "surName" with value "Messi"',
+				isCorrect: false
+			},
+			{
+				id: 4,
+				case: [
+					`user.noInternationTrophy = true`,
+					`user.noInternationTrophy = true;`,
+					`user['noInternationTrophy'] = true`,
+					`user['noInternationTrophy'] = true;`,
+					`user["noInternationTrophy"] = true`,
+					`user["noInternationTrophy"] = true;`,
+				],
+				hint: 'Add property "noInternationalTrophy" with value true',
+				isCorrect: false
+			},
+			{
+				id: 5,
+				case: [
+					`user.name = 'Leo'`,
+					`user.name = 'Leo';`,
+					`user.name = "Leo"`,
+					`user.name = "Leo";`,
+					`user['name'] = 'Leo'`,
+					`user['name'] = 'Leo';`,
+					`user['name'] = "Leo"`,
+					`user['name'] = "Leo";`,
+					`user["name"] = 'Leo'`,
+					`user["name"] = 'Leo';`,
+					`user["name"] = "Leo"`,
+					`user["name"] = "Leo";`,
+				],
+				hint: 'Change the value of the name to "Leo"',
+				isCorrect: false
+			},
+			{
+				id: 6,
+				case: [
+					'delete user.noInternationTrophy',
+					'delete user.noInternationTrophy;',
+					`delete user['noInternationTrophy']`,
+					`delete user['noInternationTrophy'];`,
+					'delete user["noInternationTrophy"]',
+					'delete user["noInternationTrophy"];',
+				]
+			}
+		]
+---
+
+`Objects` are used to store keyed collections of various data and more complex entities. In JavaScript, objects penetrate almost every aspect of the language. So we must understand them first before going in-depth anywhere else.
+
+An object can be created with figure brackets `{…}` with an optional list of _properties_. A property is a “key: value” pair, where `key` is a string (also called a “property name”), and `value` can be anything.
+
+An empty object (“empty cabinet”) can be created using one of two syntaxes:
+
+```javascript
+let user = new Object(); // "object constructor" syntax
+let user = {};  // "object literal" syntax
+```
+
+## Literals and Properties
+
+A `property` has a key (also known as “name” or “identifier”) before the colon `:` and a value to the right of it.
+
+```javascript
+let user = {     // an object
+  name: "John",  // by key "name" store value "John"
+  age: 23        // by key "age" store value 23
+};
+```
+
+In the `user` object, there are two properties:
+
+1. The first property has the name `name` and the value 'John'.
+2. The second one has the name `age` and the value 23.
+
+We can add, remove and read files from it any time.
+
+Property values are accessible using the `dot` notation:
+
+```javascript
+// get property values of the object:
+console.log( user.name ); // John
+console.log( user.age ); // 23
+```
+
+The value can be of any type. Let’s add a boolean one:
+
+```javascript
+user.isAdmin = true;
+```
+
+To remove a property, we can use `delete` operator:
+
+```javascript
+delete user.age;
+```
+
+We can also use multiword property names, but then they must be quoted:
+
+```javascript
+let user = {
+  name: "John",
+  age: 23,
+  "likes birds": true  // multiword property name must be quoted
+};
+```
+
+## Square brackets
+
+For multiword properties, the `dot` access doesn’t work. There’s an alternative “square bracket notation” that works with any string:
+
+```javascript
+// this would give a syntax error
+user.likes birds = true
+
+// correct
+user["likes birds"] = true;
+
+// alternate way
+let key = "likes birds";
+
+// same as user["likes birds"] = true;
+user[key] = true;
+console.log(user[key]); // true
+console.log(user.key); // undefined since user doesn't have the property key
+```
+
+## Computed Properties
+
+We can use square brackets in an object literal, when creating an object. That’s called computed properties.
+
+For instance:
+
+```javascript
+let key = 'email';
+
+let user = {
+	name: 'John',
+	age: 23,
+	[key]: '[email protected]'
+}
+
+console.log(user.email); // [email protected]
+```
+
+## Property value shorthand
+
+```javascript
+function makeUser(name, age) {
+  return {
+    name, // same as name: name
+    age,  // same as age: age
+    // ...
+  };
+}
+
+let user = makeUser("John", 23);
+console.log(user.name); // John
+console.log(user.age); // 23
+```
+
+## Property existence test, `in` operator
+
+Reading a non-existing property just returns undefined. So we can easily test whether the property exists. Just comparing the property value with undefined will tell you whether the property exists in that particular object or not. However, there's a special operator `in` which does the exact thing and makes our lives easier:
+
+```javascript
+let key = 'age';
+console.log('name' in user); // true
+console.log(key in user); // true
+console.log('key' in user); // false
+```
+
+Why `in`? Consider the following example:
+
+```javascript
+let test = {
+	key: undefined
+}
+
+console.log(test.key !== undefined); // false
+console.log('key' in test); // true
+```
+
+Here, the object `test` does have the property key. But comparing `test.key` with undefined implies that `test` doesn't have the property `key`. That is not true. Using the `in` operator, we get the expected result.
+
+## The for...in loop
+
+To walk over all keys of an object, there exists a special form of the loop: `for..in`. This is a completely different thing from the `for` loop construct that we studied before.
+
+The syntax, followed by an example:
+
+```javascript
+for (key in object) {
+  // executes the body for each key among object properties
+}
+
+let user = {
+	name: 'John',
+	age: 23,
+	isAdmin: true
+}
+
+for (let key in user) {
+  // keys
+  alert( key );  // name, age, isAdmin
+  // values for the keys
+  alert( user[key] ); // John, 23, true
+}
+```
+
+---
+
+## Complete the tasks below:
+
+- Create an empty object `user` using `let`.
+
+- Add the property `name` with the value 'Lionel'.
+
+- Add the property `surname` with the value 'Messi'.
+
+- Add the property `noInternationalTrophy` with the value `true`.
+
+- Change the value of `name` to 'Leo'.
+
+- Change the value of `noInternationalTrophy` to `false`. 
+
+- Remove the property `noInternationalTrophy` from the object.

courses/meta.js

@@ -53,31 +53,36 @@ let courses = [
       },
       {
         chapterId: 10,
+        chapterUrl: "objects",
+        chapterName: 'Objects'
+      },
+      {
+        chapterId: 11,
         chapterUrl: "prototypes",
         chapterName: "Prototypes"
       },
       {
-        chapterId: 11,
+        chapterId: 12,
         chapterUrl: "function",
         chapterName: "Function"
       },
       {
-        chapterId: 12,
+        chapterId: 13,
         chapterUrl: "type-conversion",
         chapterName: "Type Conversion"
       },
       {
-        chapterId: 13,
+        chapterId: 14,
         chapterUrl: "arrow-functions",
         chapterName: "Arrow Functions"
       },
       {
-        chapterId: 14,
+        chapterId: 15,
         chapterUrl: "asynchronous-behaviour-and-event-loop",
         chapterName: "Asynchronous Behaviour And Event Loop"
       },
       {
-        chapterId: 15,
+        chapterId: 16,
         chapterUrl: "foreach-map-filter",
         chapterName: "Foreach vs Map vs Filter"
       }