Introduction

When a return statement is called in a function, the execution of this function is stopped. If specified, a given value is returned to the function caller. If the expression is omitted, undefined is returned instead.

    return expression;

Functions can return:

  • Primitive values (string, number, boolean, etc.)
  • Object types (arrays, objects, functions, etc.)

Never return something on a new line without using parentheses. This is a JavaScript quirk and the result will be undefined. Try to always use parentheses when returning something on multiple lines.

function foo() {
    return 
      1;
}

function boo() {
    return (
      1
    );
}

foo(); --> undefined
boo(); --> 1

Examples

The following function returns the square of its argument, x, where x is a number.

    function square(x) {
       return x * x;
    }
:rocket:

Run Code

The following function returns the product of its arguments, arg1 and arg2.

    function myfunction(arg1, arg2){
       var r;
       r = arg1 * arg2;
       return(r);
    }
:rocket:

Run Code

When a function returns a value, the value can be assigned to a variable using the assignment operator (=). In the example below, the function returns the square of the argument. When the function resolves or ends, its value is the returned value. The value is then assigned to the variable squared2.

    function square(x) {
        return x * x;
    }
    
    let squared2 = square(2); // 4

If there is no explicit return statement, meaning the function is missing the return keyword, the function automatically returns undefined.

In the following example, the square function is missing the return keyword. When the result of calling the function is assigned to a variable, the variable has a value of undefined.

    function square(x) {
        let y = x * x;
    }
    
    let squared2 = square(2); // undefined
:rocket:

Run Code