Why Google Chrome Console Throws "syntaxerror: Unexpected Token }" When Inputted (

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

Solution 1:

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) || {}) {
    <yourcodehere>
};

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 valueundefined

> }!{ // !{} === falsefalse

> }!!{ // !!{} === truetrue

> } +{ valueOf: function() { return123; }
  123