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();

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

The returned value can be used anywhere a value is expected.

You can use a function call inside another expression.

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 NOT be executed.

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

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.