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
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);The value of result is undefined .
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
Returned function values are often used to update HTML content.
Example
<p id="demo"></p> <script> function toCelsius(farenheit) {
return (5 / 9) * (farenheit - 32);
}
document.getElementById("demo").innerHTML = toCelsius(77);
</script>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 .
Expecting Return
Function Arguments
- Function parameters and arguments are distinct concepts
- Parameters are the names listed in the function definition
- Arguments are the values received by the function