Functions: Code Blocks for Specific Tasks

A function is a reusable block of code that performs a specific task.

To create a function, you group one or more lines of code within curly braces { }, forming a block, and give it a name.

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function sayHello() {
  console.log('Hello');
  console.log('Nice to meet you');
}

The above function is named sayHello to represent its purpose: printing the messages 'Hello' and 'Nice to meet you'.

Two console.log statements are written inside the function, and the { } curly braces form a single block.

When the function is called, the code inside the function runs, printing the messages 'Hello' and 'Nice to meet you' line by line.

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sayHello(); // Outputs 'Hello' and 'Nice to meet you'

The primary purpose of a function is to improve code reusability.

Once a function is defined, it can be called multiple times using its name. This reduces code duplication and improves maintainability.

In JavaScript, you define a function using the function keyword, followed by the function name and parameters.

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function add(a, b) {
  return a + b;
}

Here, add is the function's name, and a and b are its parameters.

Inside the curly braces { }, you write the code the function will execute. The return keyword is used to return the result of the function.

Calling a function means executing the code inside it.

You call a function by writing its name followed by parentheses ().

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const result = add(10, 20); // 30

In the above code, add(10, 20) calls the add function, passing 10 and 20 as arguments.

When the function is called, the parameters a and b receive the values 10 and 20, and the function executes.

The return a + b line inside the function calculates 30 and returns it.

The returned value, 30, is stored in the constant result.

• Parameters are variables defined in the function declaration and used inside the function.
• Arguments are the actual values passed to the function when it is called.

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function multiply(a, b) {
  return a * b;
}

const result = multiply(2, 3); // 6

For example, in the multiply function, a and b are parameters, while 2 and 3 are the arguments passed when the function is called.