12.2) Logical Operations.js

3) Comprehensive Challenge - Logical operations (AND/OR):
If the number is less than or equal to 10 and the string has a length greater than or equal to 5, or if the boolean is true, 
log true to the console, else log false.

Use the following to test the code:
number = 10;
string = "hi";
boolean = true;

Solution:
const givenNumber = 10;
const givenString = "hi";
const givenBoolean = true;

if (givenNumber <= 10 && givenString.length >= 5 || givenBoolean === true) {
  console.log(true);
}
else {
  console.log(false);
}

4) NOT ('!'):
The NOT operator - !, when applied to a value or expression returns false if the condition evaluates to true and returns true if the condition evaluates to false.

For example, let's say we have an object user with two properties - name and isAdmin. 
Let's say we need to display "You do not have access to this feature", if the value of user.isAdmin is false. 
The following example shows how to use the ! operator to perform this check:

const user = {
  name: "Oliver Smith",
  isAdmin: false,
};

if (!user.isAdmin===true) {
  console.log("You do not have access to this feature");
}

In the example given above, user.isAdmin is false and the condition !user.isAdmin returns true. 
If the value of user.isAdmin was true, then the condition !user.isAdmin would result in false. 

NOT table:
user.isAdmin	Result
true	        false
false	        true

Example 2:
Write an if statement, that displays "Who are you?" if the value of the variable personName is "", provided that the value of personName will always be of the type string.

Solution:
const personName = "";

if(!personName !== "") {
  console.log("Who are you?");
};

5) Inequality Operators: used to compare two values and check whether they are not equal.

Example:
Let's say we need to display "You get a 10% discount on your course fee" when student.grade is not "D" and student.nationality is not "India". 
Since we need to make two comparisons here, it is fine to use the ! operator as shown below.
const student = {
  grade: "A",
  nationality: "Indian",
};

if (!(student.grade === "D" && student.nationality === "India")) {
  console.log("You get a 10% discount on your course fee");
}

6) Nullish Coalescing Operator:

a) The Nullish Coalescing operator, denoted as ??, returns the left-hand operand provided that the left-hand operand is not null or undefined. 
Otherwise, it returns the right-hand operand.

Solution:
console.log("Hello Sam Smith" ?? "Hello Guest");
console.log(null ?? "Hello Guest");
console.log(undefined ?? "Hello Guest");
console.log(0 ?? 234);
console.log(false ?? true);
console.log(undefined ?? null); //If the value on the left-hand side of the ?? operator is either null or undefined, the operator will return the value on the right-hand side.
console.log(null ?? null);

b) const defaultRole = "Standard";:

  Example 1: 
  const user1 = {
  name: "Sam Smith",
  age: 32,
  role: "Admin",
};
console.log(`${user1.name} is a ${user1.role} user.`);

const user2 = {
  name: "Oliver Smith",
  age: 32,
};
console.log(`${user2.name} is a ${user2.role} user.`);

* user2.role --> undefined! to remove undefined, will place: const defaultRole = "Standard";
in the beginning, so that whenever there's a chance to get undefined, will get standard!

Example 2:
const defaultRole = "Standard";

const user1 = {
  name: "Sam Smith",
  age: 32,
  role: "Admin",
};
console.log(`${user1.name} is a ${user1.role ?? defaultRole} user.`);

const user2 = {
  name: "Oliver Smith",
  age: 32,
};
console.log(`${user2.name} is a ${user2.role ?? defaultRole} user.`);

c) Challenge:
In the example given below, user2 does not have the property noOfAttempts, which causes an unwanted output when totalNoOfAttempts - user2.noOfAttempts is executed.
Use the ?? operator to use the default value of the noOfAttempts as 0.

Solution:
const defaultRole = 0;

const totalNoOfAttempts = 5;

const user1 = {
  name: "Sam Smith",
  noOfAttempts: 3,
};

const user2 = {
  name: "Oliver Smith",
};

console.log(`${user1.name} has ${totalNoOfAttempts - (user1.noOfAttempts ?? defaultRole)} attempts left.`);
console.log(`${user2.name} has ${totalNoOfAttempts - (user2.noOfAttempts ?? defaultRole)} attempts left.`);