{}.toString() 未捕获的语法错误:意外的令牌 [英] {}.toString() Uncaught SyntaxError: Unexpected token

问题描述

当我在 chrome 开发工具中尝试时，它显示Uncaught SyntaxError: Unexpected token .但是，如果它分配给a:

when I try it in chrome dev tools, it shows Uncaught SyntaxError: Unexpected token . However if when it assign to a:

var a={}.toString(); 
a //[object Object]

是什么导致了差异?

推荐答案

是什么导致了差异?

what caused the difference?

解析器所处的状态.默认情况下，解析器处于期望语句的状态.因此，在控制台中的示例中， { 看起来像是对它的块的打开，而不是对象初始值设定项的开始.(此时你也可以给它一个表达式，因为 JavaScript 有 ExpressionStatement 的概念，它是一个完全由表达式组成的语句.)

The state the parser is in. By default, the parser is in a state where it expects a statement. So in your example in the console, the { looks like the opening of a block to it, not the beginning of an object initializer. (You can also give it an expression at that point, because JavaScript has the concept of the ExpressionStatement, which is a statement consisting entirely of an expression.)

但是在您的 var a={}.toString(); 代码中，{}.toString() 出现在赋值的右侧，解析器需要一个表达式，而不是一个语句.所以 { 启动一个对象初始值设定项.

But in your var a={}.toString(); code, the {}.toString() appears on the right-hand side of an assigment, where the parser is expecting an expression, not a statement. So the { starts an object initializer.

如果你做一些事情让解析器期待一个表达式，它也可以在控制台中工作:

If you do something to make the parser expect an expression instead, it'll work in the console too:

({}).toString(); // "[object Object]"

或

+{}.toString(); // NaN, because the `+` tries to turn `[object Object]` into a number and fails

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