语法错误：丢失的 ; 声明之前

¥Message

SyntaxError: Expected ';' (Edge)
SyntaxError: missing ; before statement (Firefox)

¥Error type

SyntaxError。

¥What went wrong?

某处缺少分号 (;)。JavaScript 语句 必须以分号终止。其中一些受到 自动分号插入 (ASI) 的影响，但在这种情况下你需要提供分号，以便 JavaScript 可以正确解析源代码。

¥There is a semicolon (;) missing somewhere. JavaScript statements must be terminated with semicolons. Some of them are affected by automatic semicolon insertion (ASI), but in this case you need to provide a semicolon, so that JavaScript can parse the source code correctly.

但是，通常情况下，此错误只是另一个错误的结果，例如未正确转义字符串或错误地使用 var。你也可能在某个地方有太多括号。抛出此错误时请仔细检查语法。

¥However, oftentimes, this error is only a consequence of another error, like not escaping strings properly, or using var wrongly. You might also have too many parenthesis somewhere. Carefully check the syntax when this error is thrown.

¥Examples

¥Unescaped strings

当未正确转义字符串且 JavaScript 引擎已预期字符串结尾时，很容易发生此错误。例如：

¥This error can occur easily when not escaping strings properly and the JavaScript engine is expecting the end of your string already. For example:

const foo = 'Tom's bar';
// SyntaxError: missing ; before statement

你可以使用双引号，或转义撇号：

¥You can use double quotes, or escape the apostrophe:

const foo = "Tom's bar";
// OR
const foo = 'Tom\'s bar';

¥Declaring properties with keyword

不能使用 let、const 或 var 声明来声明对象或数组的属性。

¥You cannot declare properties of an object or array with a let, const, or var declaration.

const obj = {};
const obj.foo = "hi"; // SyntaxError missing ; before statement

const array = [];
const array[0] = "there"; // SyntaxError missing ; before statement

相反，省略关键字：

¥Instead, omit the keyword:

const obj = {};
obj.foo = "hi";

const array = [];
array[0] = "there";

¥Bad keywords

如果你来自另一种编程语言，那么在 JavaScript 中使用含义不同或根本没有含义的关键字也很常见：

¥If you come from another programming language, it is also common to use keywords that don't mean the same or have no meaning at all in JavaScript:

def print(info) {
  console.log(info);
} // SyntaxError missing ; before statement

相反，使用 function 而不是 def：

¥Instead, use function instead of def:

function print(info) {
  console.log(info);
}

¥See also

• 自动分号插入 (ASI)
• 语句和声明