SyntaxError: Unexpected token

The JavaScript exceptions "unexpected token" occur when a specific language construct was expected, but something else was provided. This might be a simple typo.

Message

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"

Error type

SyntaxError

What went wrong?

A specific language construct was expected, but something else was provided. This might be a simple typo.

Examples

Expression expected

For example, when chaining expressions, trailing commas are not allowed.

js

for (let i = 0; i < 5,; ++i) {
  console.log(i);
}
// Uncaught SyntaxError: expected expression, got ';'

Correct would be omitting the comma or adding another expression:

js

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

Not enough brackets

Sometimes, you leave out brackets around if statements:

js

function round(n, upperBound, lowerBound) {
  if (n > upperBound) || (n < lowerBound) { // Not enough brackets here!
    throw new Error(`Number ${n} is more than ${upperBound} or less than ${lowerBound}`);
  } else if (n < (upperBound + lowerBound) / 2) {
    return lowerBound;
  } else {
    return upperBound;
  }
} // SyntaxError: expected expression, got '||'

The brackets may look correct at first, but note how the || is outside the brackets. Correct would be putting brackets around the ||:

js

function round(n, upperBound, lowerBound) {
  if ((n > upperBound) || (n < lowerBound)) {
    throw new Error(
      `Number ${n} is more than ${upperBound} or less than ${lowerBound}`,
    );
  } else if (n < (upperBound + lowerBound) / 2) {
    return lowerBound;
  } else {
    return upperBound;
  }
}

See also