The Problem

The SyntaxError: missing ) after argument list is a very common syntax error in JavaScript. As its name suggests, it means that the JavaScript parser expected a closing parenthesis ) after a function’s argument list, but did not find one.

When the JavaScript engine parses your code, it recognizes a function call when it sees an opening parenthesis ( after a function name. It then reads the list of arguments until it finds a matching closing parenthesis ). If the closing parenthesis is missing from its expected position, the engine determines that the syntax is incomplete and throws this error.

Examples of Error-Prone Code

The most typical example is simply forgetting the closing parenthesis in a function call.

console.log("Hello, World!";
// SyntaxError: missing ) after argument list

In the code above, the console.log function receives the argument "Hello, World!", but it is immediately followed by a semicolon ; instead of a closing parenthesis ).

This error can be harder to spot when function calls are nested or the code is more complex.

// The closing parenthesis for the alert function is missing.
alert(parseInt("123" ); 
// SyntaxError: missing ) after argument list

How to Fix It

Since this is a syntax issue, the solution is very straightforward.

1. Add the Missing Closing Parenthesis )

Check the line where the error occurred and add the missing closing parenthesis ) at the end of the function’s argument list.

// Corrected code
console.log("Hello, World!");

alert(parseInt("123"));

2. Use Your Code Editor’s Help

To reduce these kinds of mistakes, it’s highly recommended to leverage the features of your code editor (e.g., VS Code).

  • Bracket Matching: Most editors automatically add a closing parenthesis when you type an opening one. They also highlight matching pairs, making it easy to spot a missing one.
  • Use a Linter: A tool like ESLint can detect syntax errors in real-time as you write code, often underlining the problematic area. This allows you to fix the issue before you even run the code.
  • Use a Code Formatter: A tool like Prettier automatically formats your code into a consistent style whenever you save. As the code is aligned, its structure becomes clearer, making a missing parenthesis more visually apparent.

Conclusion

The SyntaxError: missing ) after argument list is a syntax error caused by simple carelessness. If you encounter this error, don’t panic. Just check the following:

  • Look at the function call on the line where the error occurred.
  • Ensure that a closing parenthesis ) is correctly placed after the argument list.

In most cases, the problem is solved by adding a single missing parenthesis. Using your editor’s built-in features can greatly help in preventing these errors from happening in the first place.

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