为什么Google Chrome控制台会抛出“SyntaxError:Unexpected token}”当输入时( [英] Why Google Chrome console throws "SyntaxError: Unexpected token }" when inputted (
问题描述
(
和Enter,Chrome说SyntaxError:Unexpected token}为什么?输入只是(,包括没有}。
当我们输入
console.log(
没有}!!!
下一个标记应该是参数列表或),所以错误消息应该是预期的参数列表或未关闭(或什么。
)我想知道,是控制台输入解析为 StatementList(opt)
(在ECMA-262中定义)?
编辑:我找到了得到评估的确切代码,代码位于src / third_party / WebKit / Source / WebCore / inspector / InjectedScriptSource.js中。
在Chrome控制台评估您的代码之前,它会使用块将其封装到中,以将命令行功能纳入范围。实际上是在大括号内进行评估。这个意外的}令牌是Chrome自动发布的令牌。
Chrome传递给 eval
((window& window.console&& window.console._commandLineAPI)|| {b
$ b
){
<您的代码在这里>
};
因为它是一个简单的文本替换,所以下面的例子可以工作,结果是一个可以扩展的对象查看答案
属性:
} 0,{answer:42
其中(重新格式化)等同于:
< ((window& window.console&& window.console._commandLineAPI)|| {}){
}
0,{pre> 答案:42};
开始时的}
code>与块。 0,
部分对于强制对象文本被解析为表达式而不是另一个块是必需的。然后, {answer:42
是被插入的}
标记关闭的对象字面值的开始。 / p>
为获得更多乐趣,以下是其他一些可用的输入(及其结果):
> } {//空块,所以没有值
undefined
> }!{//!{} === false
false
> } !! {// !! {} === true
true
> } + {valueOf:function(){return 123; }
123
In Google Chrome's console, when we input
(
and Enter, Chrome says "SyntaxError: Unexpected token }" Why? Input is just "(", including no "}".
We get the same error when we input
console.log(
There's no "}"!!!
Next token should be arguments list or ")" so error message should be "Expected arguments list" or "Unclosed (" or something.
And I wanna know, is console input parsed as StatementList(opt)
(defined in ECMA-262)?
Edit: I found the exact code that gets evaluated. The code is in "src/third_party/WebKit/Source/WebCore/inspector/InjectedScriptSource.js".
Before the Chrome console evaluates your code, it wraps it in a with
block to bring the command-line functions into scope. So what you type is actually evaluated inside braces. The unexpected "}" token is the one put in automatically by Chrome.
The code that Chrome passes to eval
is
with ((window && window.console && window.console._commandLineAPI) || {}) {
<your code here>
};
Because it's a simple text substitution, the following example works and the result is an object which you can expand to see the answer
property:
} 0, { answer: 42
Which (reformatted) is equivalent to:
with ((window && window.console && window.console._commandLineAPI) || {}) {
}
0, { answer: 42 };
The }
at the beginning closes the with
block. The 0,
part is necessary to force the object literal to be parsed as an expression instead of another block. Then, the { answer: 42
is the beginning of an object literal that gets closed by the inserted }
token.
For more fun, here are some other inputs that work (and their results):
> }{ // an empty block, so no value
undefined
> }!{ // !{} === false
false
> }!!{ // !!{} === true
true
> } +{ valueOf: function() { return 123; }
123
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