SyntaxError: Unexpected token
The JavaScript exceptions "unexpected token" occur when the parser does not see a token it recognizes at the given position, so it cannot make sense of the structure of the program. This might be a simple typo.
Message
SyntaxError: Unexpected token ';' (V8-based)
SyntaxError: Unexpected identifier 'x' (V8-based)
SyntaxError: Unexpected number (V8-based)
SyntaxError: Unexpected string (V8-based)
SyntaxError: Unexpected regular expression (V8-based)
SyntaxError: Unexpected template string (V8-based)
SyntaxError: unexpected token: identifier (Firefox)
SyntaxError: expected expression, got "x" (Firefox)
SyntaxError: expected property name, got "x" (Firefox)
SyntaxError: expected target, got "x" (Firefox)
SyntaxError: expected meta, got "x" (Firefox)
SyntaxError: expected rest argument name, got "x" (Firefox)
SyntaxError: expected closing parenthesis, got "x" (Firefox)
Error type
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.
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:
for (let i = 0; i < 5; ++i) {
console.log(i);
}
Not enough parentheses
Sometimes, you leave out parentheses around if
statements:
function round(n, upperBound, lowerBound) {
if (n > upperBound) || (n < lowerBound) { // Missing parentheses 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 parentheses may look correct at first, but note how the ||
is outside the
parentheses. Correct would be putting parentheses around the ||
:
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;
}
}