This JavaScript exception return (or yield) not in function occurs if a return/yield statement is written outside the body of the function.

Message:

SyntaxError: 'return' statement outside of function (Edge)
SyntaxError: return not in function (Firefox)
SyntaxError: yield not in function (Firefox)

Error Type:

SyntaxError

What happened?

Either the return or yield statement is called outside the body of the function or there might be a missing curly bracket in the code.

Case 1: Return Statement Outside of Function

Error Cause:

The most common cause is using the return statement outside of a function, which leads to a syntax error.

Example:

return 5; // Incorrect usage, not inside a function

Output:

SyntaxError: Illegal return statement

Resolution of Error:

Ensure that the return statement is inside a function.

function exampleFunction() {
    return 5; // Correct usage, inside a function
}
console.log(exampleFunction()); // Outputs: 5

5

Case 2: Misplaced Return in Global Code

Error Cause:

Another cause is placing the return statement in the global scope or in an incorrect context.

Example:

return "Hello, world!"; // Incorrect usage, in the global scope

Output:

SyntaxError: Illegal return statement

Resolution of Error:

Move the return statement into a function.

function greet() {
    return "Hello, world!"; // Correct usage, inside a function
}
console.log(greet()); // Outputs: Hello, world!

Hello, world!

Case 3: Return Statement in a Non-function Block

Error Cause:

Using a return statement inside blocks that are not functions, such as conditionals or loops, will also result in an error.

Example:

if (true) {
    return "This will cause an error."; // Incorrect usage, inside an if block
}

Output:

SyntaxError: Illegal return statement

Resolution of Error:

Ensure that the return statement is used only within a function.

function checkCondition() {
    if (true) {
        return "Condition met"; // Correct usage, inside a function
    }
}
console.log(checkCondition()); // Outputs: Condition met

Condition met