JavaScript SyntaxError - Missing formal parameter

This JavaScript exception missing formal parameter occurs if any function declaration doesn't have the valid parameters.

Message:

SyntaxError: missing formal parameter (Firefox)

Error Type:

SyntaxError

Cause of Error: The function declaration is missing the formal parameters.

Case 1: Incorrect Function Syntax

Error Cause:

A common cause is incorrect function syntax, such as using a comma without a following parameter name.

Example:

function exampleFunction(a, , b) {
    return a + b;
}
console.log(exampleFunction(1, 2));

Output:

SyntaxError: Missing formal parameter

Resolution of Error:

Ensure that all parameters are correctly defined and separated by commas.

function exampleFunction(a, b) {
    return a + b;
}
console.log(exampleFunction(1, 2)); // Correct usage

3

Case 2: Arrow Function with Missing Parameter

Error Cause:

An arrow function with missing parameters can also cause this error.

Example:

const exampleFunction = (a, , b) => a + b;
console.log(exampleFunction(1, 2));

Output:

SyntaxError: Missing formal parameter

Resolution of Error:

Ensure that all parameters are correctly defined.

const exampleFunction = (a, b) => a + b;
console.log(exampleFunction(1, 2)); // Correct usage

3

Case 3: Function Constructor with Missing Parameter

Error Cause:

Using the Function constructor with incorrect parameters can lead to this error.

Example:

const exampleFunction = new Function('a', '', 'b', 'return a + b');
console.log(exampleFunction(1, 2));

Output:

SyntaxError: Missing formal parameter

Resolution of Error:

Ensure that all parameters are correctly defined in the Function constructor.

const exampleFunction = new Function('a', 'b', 'return a + b');
console.log(exampleFunction(1, 2)); // Correct usage

3