Returning vs. Logging

It’s important to understand thatreturn and print are not the same thing. Printing a value to the JavaScript console only displays a value (that you can view for debugging purposes), but the value it displays can't really be used for anything more than that. For this reason, you should remember to only useconsole.logto test your code in the JavaScript console.

Paste the following function declaration_and_function invocation into the JavaScript console to see the difference between logging (printing) and returning:

function isThisWorking(input) {
  console.log("Printing: isThisWorking was called and " + input + " was passed in as an argument.");
  return "Returning: I am returning this string!";
}

isThisWorking(3);

Prints:"Printing: isThisWorking was called and 3 was passed in as an argument"
Returns:"Returning: I am returning this string!"

If you don't explicitly define a return value, the function will returnundefinedby default.

function isThisWorking(input) {
  console.log("Printing: isThisWorking was called and " + input + " was passed in as an argument.");
}

isThisWorking(3);

Prints:"Printing: isThisWorking was called and 3 was passed in as an argument"
Returns:undefined

Using Return Values

Returning a value from a function is great, but what's the use of a return value if you're not going to use the value to do something?

A function's return value can be stored in a variable or reused throughout your program as a function argument. Here, we have a function that adds two numbers together, and another function that divides a number by 2. We can find the average of 5 and 7 by using theadd()function to add a pair of numbers together, and then by passing the sum of the two numbersadd(5, 7)into the functiondivideByTwo()as an argument.

And finally, we can even store the final answer in a variable calledaverageand use the variable to perform even more calculations in more places!

// returns the sum of two numbers
function add(x, y) {
  return x + y;
}


// returns the value of a number divided by 2
function divideByTwo(num) {
  return num / 2;
}


var sum = add(5, 7); // call the "add" function and store the returned value in the "sum" variable
var average = divideByTwo(sum); // call the "divideByTwo" function and store the returned value 
                                // in the "average" variable