Scope Variable and Recursion

 

Variable Scope

• Two types of scopes in JavaScript.

1. Global Scope

2. Local Scope

Global Scope

• Variable declared out of the function is called global scope.

• Global Variable can be used anywhere in the program. 

// Global variable

let name = "Hello";

// declaring the function

function fullName(){

    console.log(name);

}

fullName();

• variable name is a global variable. It means the variable name can be used anywhere in the program.

• The value of global variable can be changed in inside the function

// Global variable

let name = "Hello";

// declaring the function

 function fullName() {

  name = "Welcome"

   console.log(name); //Welcome

}

// calling the function

fullName();

Local Scope

•  variable declared inside the function is called local scope.

•  variable cannot be accessed outside the function.

// program showing local scope of a variable

//Global Variable

let a = "hello";

function greet() {

    // Local Variable

    let b = "World"

    console.log(a + b);

}

greet();

console.log(a + b); // error

• variable a is a global variable and variable b is a local variable.

• The variable b can be accessed only inside the function greet.

• when we try to access variable b outside of the function, an error occurs.

JavaScript Recursion

• Recursion is a process of calling itself. A function that calls itself is called a recursive function.

• The syntax for the recursive function is

function recurse() {

    // function code

    recurse();

    // function code

}

recurse();

• recurse() function is a recursive function. It is calling itself inside the function.

• A recursive function must have a condition to stop calling itself. Otherwise, the function is called indefinitely.

• Once the condition is met, the function stops calling itself. This is called a base condition.

• To prevent infinite recursion, you can use if...else statement (or a similar approach) where one branch makes the recursive call, and the other doesn't.

function recurse() {

    if(condition) {

        recurse();

    }

    else {

        // stop calling recurse()

    }

}

recurse();

// program to find the factorial of a number

function factorial(x) {

    // if number is 0

    if (x === 0) {

        return 1;

    }

    // if number is positive

    else {

        return x * factorial(x - 1);

    }

}

const num = 3;

// calling factorial() if num is non-negative

if (num > 0) {

    let result = factorial(num);

    console.log(`The factorial of ${num} is ${result}`);

// Outpout:

factorial(3) returns 3 * factorial(2)

factorial(2) returns 3 * 2 * factorial(1)

factorial(1) returns 3 * 2 * 1 * factorial(0)

factorial(0) returns 3 * 2 * 1 * 1

}