Functions: Code Blocks that Perform Specific Tasks

A Function is a reusable block of code designed to perform a specific task.

For this purpose, you enclose one or more lines of code within curly braces { } to create a Block, and then give a name to this block.

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

The function above has the name sayHello and is designed to print the messages 'Hello' and 'Nice to meet you'.

Inside the function, two console.log statements are written, and these two statements are enclosed within curly braces { } to form a single block.

When the function is called, the code within the function runs and the messages 'Hello' and 'Nice to meet you' are printed line by line.

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sayHello(); // Prints 'Hello', 'Nice to meet you'

The purpose of functions is to increase the reusability of code.

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

In JavaScript, a function is defined using the function keyword along with its 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 that the function will execute. Use the return keyword to return the result of the function.

Calling a function means executing the code inside the function.

To call a function, write the function's name followed by parentheses ().

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

In the code above, add(10, 20) calls the add function, and 10 and 20 are the arguments passed to the function.

When the function is called, the arguments 10 and 20 are passed to the parameters a and b respectively, and the function executes.

Then, the code return a + b inside the function runs, returning 30.

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

Parameters are the variables used inside the function when it is defined, while arguments are the actual values passed when calling the function.

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

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

For instance, the parameters of the multiply function are a and b, while the values 2 and 3 passed when calling the function are the arguments.