Understanding
Parameters, Arguments, and Return Values

Introduction to Parameters, Arguments, and Return Values

Functions in JavaScript are reusable blocks of code that can take inputs and produce outputs. These inputs are called parameters when defining the function, and arguments when calling the function.

What Are Parameters?

Parameters are placeholders defined in a function declaration. Think of them as variables local to the function that will hold the values you pass when calling it.

function greet(name) {
  console.log("Hello, " + name + "!");
}
    

In the above example, name is the parameter.

What Are Arguments?

Arguments are the actual values you pass into the function when invoking it. These values get assigned to the parameters.

greet("Alice");
    

Output:

Hello, Alice!

Can We Pass Multiple Arguments?

Yes. You can define multiple parameters and pass corresponding arguments.

function add(a, b) {
  console.log("Sum:", a + b);
}

add(5, 7);
    

Output:

Sum: 12

What If We Pass Fewer or More Arguments?

If fewer arguments are passed, the missing ones become undefined. If more are passed, the extra ones are ignored unless handled using the arguments object or rest parameters.

function display(a, b) {
  console.log("a =", a);
  console.log("b =", b);
}

display(1); // only one argument
    

Output:

a = 1
b = undefined

What Is a Return Value?

A function can also return a value using the return keyword. This allows the function to pass a result back to where it was called.

function multiply(x, y) {
  return x * y;
}

let result = multiply(4, 5);
console.log("Result:", result);
    

Output:

Result: 20

How Do Return Statements Work?

The return statement ends function execution and specifies the value to be returned. If there's no return, the function returns undefined.

function sayHi() {
  console.log("Hi there!");
}

let res = sayHi();
console.log("Return value:", res);
    

Output:

Hi there!
Return value: undefined

Question for Intuition:

Question: Can a function both return a value and print a message?

Answer: Yes! You can use console.log() for displaying messages and return for sending back a value.

function doubleIt(n) {
  console.log("Doubling", n);
  return n * 2;
}

let doubled = doubleIt(10);
console.log("Doubled value is:", doubled);
    

Output:

Doubling 10
Doubled value is: 20

Using Return Values in Expressions

You can use return values in larger expressions or pass them to other functions.

function square(n) {
  return n * n;
}

console.log("Square of 6 plus 1 is:", square(6) + 1);
    

Output:

Square of 6 plus 1 is: 37

Conclusion

Understanding parameters, arguments, and return values is fundamental to writing reusable and effective functions in JavaScript. Parameters are defined in the function, arguments are the actual values passed in, and return values give you back a result that can be used further.