语法错误: 意外的标记
JavaScript 异常 "unexpected token" 发生在解析器在给定位置没有看到它识别的标记时,因此无法理解程序的结构。这可能是一个简单的拼写错误。
消息
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)
错误类型
出了什么问题?
预期特定语言结构,但提供了其他内容。这可能是一个简单的拼写错误。
示例
预期表达式
例如,在连接表达式时,不允许尾随逗号。
js
for (let i = 0; i < 5,; ++i) {
console.log(i);
}
// Uncaught SyntaxError: expected expression, got ';'
正确的是省略逗号或添加另一个表达式
js
for (let i = 0; i < 5; ++i) {
console.log(i);
}
括号不足
有时,您会在 `if` 语句周围省略括号
js
function round(n, upperBound, lowerBound) {
if (n > upperBound) || (n < lowerBound) { // Not enough parenthese 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 '||'
括号乍一看可能是正确的,但请注意 `||` 如何在括号之外。正确的是将括号放在 `||` 周围
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;
}
}