JavaScript Function Return

Returning Values from Functions

A function can return a value back to the code that called it.
The return statement is used to send a value out of a function.

The return

Statement

When a function reaches a return statement, the function stops executing.
The value after the return keyword is sent back to the caller.

Example function sayHello() {
return "Hello World";
}
let message = sayHello();
The variable message now contains "

Hello World

Returning a Calculated Value

Most functions return the result of a calculation or an operation.

Example function multiply(a, b) {
return a * b;
}
let result = multiply(4, 5);

Using Return Values in Expressions

Example function multiply(a, b) {
return a * b;
}
let total = multiply(2, 3) * 10;

Return Values

A function can return any type of value (not only numbers).

Example function fullName(firstName, lastName) {
return firstName + " " + lastName;
}
let name = fullName("John", "Doe");

Return Statements Stop Execution

Code written after a return statement will

Example function multiply(a, b) {
return "Done";
// Next line will never run return a * b;
}
let result = multiply(4, 3);

Functions Without return

If a function does not return a value, the return value will be undefined.

Example function multiply(a, b) {
let x = a * b;
}
let result = multiply(4, 3);

Returning Values Early

You can use return to stop a function early, based on a condition.

Example function checkAge(age) {
if (age < 18) {
return "Too young";
}
return "Access granted";
}

Returning Values to HTML

Example

function toCelsius(farenheit) {
return (5 / 9) * (farenheit - 32);
}
document.getElementById("demo").innerHTML = toCelsius(77);

Common Mistakes

Forgetting Return

A function without return sends back undefined.

Expecting Code after Return to Run

Code after return is ignored.
Confusing console.log() with Return console.log()
shows output but does not return a value.

Expecting Return

If your function does not return a value, storing it in a variable will give undefined.

Next Chapter

Function Arguments

Function parameters and arguments are distinct concepts