How to Fix JavaScript SyntaxError: Unexpected token

In this tutorial, you'll learn about How to Fix JavaScript SyntaxError: Unexpected token. We cover key concepts, practical examples, and best practices.

The Problem

JavaScript throws SyntaxError: Unexpected token when the parser encounters a character it does not expect. This is almost always caused by missing closing brackets, mismatched quotes, trailing commas in JSON, or stray operators.

Quick Fix

Step 1: Check for mismatched brackets

Count opening and closing braces, parentheses, and brackets:

node -e "const obj = { name: 'Alice'; }"

SyntaxError: Unexpected token ';'

The semicolon inside the object literal should be a comma:

node -e "const obj = { name: 'Alice' }; console.log(obj);"

{ name: 'Alice' }

Step 2: Fix missing closing parenthesis

A common mistake is forgetting to close a function call:

node -e "console.log('hello';"

SyntaxError: Unexpected token ';'

Add the missing closing parenthesis:

node -e "console.log('hello');"

hello

Step 3: Validate JSON with jq

If the unexpected token error comes from JSON parsing, use jq to validate:

echo '{"name": "Alice", "age": 30,}' | node -e "process.stdin.on('data', d => console.log(JSON.parse(d)))"

SyntaxError: Unexpected token '}'

Remove the trailing comma after the last property.

Step 4: Check for stray operators

A dangling operator on its own line causes an unexpected token error:

node -e "
const x = 5
+
const y = 3
"

Fix by placing the operator on the correct line:

node -e "
const x = 5 + 3
console.log(x);
"

8

Alternative Solutions

Use a linter with automatic fixing

ESLint can catch and fix syntax errors automatically:

npx eslint --fix script.js

Validate JSON with Python

Use Python for JSON validation if jq is not available:

python3 -m json.tool data.json

Common Mistakes to Avoid

Leaving trailing commas in JSON. JavaScript allows trailing commas in objects and arrays, but JSON does not. Use JSON.parse() after removing trailing commas.

Missing a comma between object properties. Each property in an object literal must be separated by a comma except the last one.

Unclosed template literals. A backtick that is not closed causes an unexpected token error that can span many lines. Match every opening backtick.

Pro Tips

Use Prettier for automatic formatting. Prettier reformats code on save, catching missing brackets, trailing commas, and indentation issues.

Run npx eslint before committing. Add a pre-commit hook that runs ESLint to catch syntax errors before they reach the repository.

Use a linter with --fix for quick corrections. ESLint's --fix flag automatically corrects many syntax issues: npx eslint --fix script.js.

Use a JSON validator extension in your editor. VS Code extensions like JSON Tools format and validate JSON files on save, catching syntax errors before they reach your JavaScript code.

Prevention

• Use a code editor with bracket matching and syntax highlighting.
• Run npx eslint . to catch syntax errors before execution.
• Lint your JSON files with jq . file.json before parsing them in code.