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.
The variable message now contains "Hello World".
Returning a Calculated Value
Most functions return the result of a calculation or an operation.
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;
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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");
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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);
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Functions Without return
If a function does not return a value, the return value will be undefined.
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";
}
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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>
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Quiz
What value is returned if a function has no return statement?
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 parameters and arguments are distinct concepts
- Parameters are the names listed in the function definition
- Arguments are the values received by the function
