How to Fix the ‘SyntaxError: Unexpected token ‘ Error in Our JavaScript App?

Sometimes, we may run into the ‘SyntaxError: Unexpected token’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘SyntaxError: Unexpected token’ when we’re developing JavaScript apps.

Fix the ‘SyntaxError: Unexpected token’ When Developing JavaScript Apps

To fix the ‘SyntaxError: Unexpected token’ when we’re developing JavaScript apps, we should make sure we’re writing JavaScript code that’s syntactically valid.

Different unexpected token errors that may be thrown include:

SyntaxError: expected expression, got "x"
SyntaxError: expected property name, got "x"
SyntaxError: expected target, got "x"
SyntaxError: expected rest argument name, got "x"
SyntaxError: expected closing parenthesis, got "x"
SyntaxError: expected '=>' after argument list, got "x"

For instance, we should make sure we aren’t adding trailing commas when we’re chaining expressions:

for (let i = 0; i < 5,; ++i) {
  console.log(i);
}

We have:

i < 5,;

which has a comma before the semicolon. This is invalid syntax.

Instead, we should write:

for (let i = 0; i < 5; ++i) {
  console.log(i);
}

which removed the extra comma.

We should also make sure that we have corresponding closing parentheses for any opening parentheses.

For example, instead of writing:

function round(n, upperBound, lowerBound){
  if(n > upperBound) || (n < lowerBound){
    throw 'Number ' + String(n) + ' is more than ' + String(upperBound) + ' or less than ' + String(lowerBound);
  }
} 

We write:

function round(n, upperBound, lowerBound) {
  if (n > upperBound || n < lowerBound) {
    throw (
      "Number " +
      String(n) +
      " is more than " +
      String(upperBound) +
      " or less than " +
      String(lowerBound)
    );
  }
}

which removes the extra parentheses from if boolean expression.

Conclusion

To fix the ‘SyntaxError: Unexpected token’ when we’re developing JavaScript apps, we should make sure we’re writing JavaScript code that’s syntactically valid.