Please explain this usage of a colon in javascript
javascript, syntax
Solution
It is a label
Provides a statement with an identifier that you can refer to using a break or continue statement.
For example, you can use a label to identify a loop, and then use the break or continue statements to indicate whether a program should interrupt the loop or continue its execution.
Another common place you see it is when people stick the wonderful and useless `javascript:` on event handlers.
Problem
I'm making a library, and I often inspect the result of Closure Compiler's output to see how it's doing things (I do have unit tests, but I still like to see the compiled code for hints of how it could compress better). So, I found this very weird piece of code, which I never seen before. ``` variable : { some(); code() } ``` Note: this is not an object literal! Also, there is no `?` anywhere that would make it a `?:` conditional. That code is in a regular function block (an IIFE). `variable`, in this case, is an undefined variable. There's no code making it true, false, or whatever, and just to make sure, I put a `console.log` in there and indeed, I get a `ReferenceError`. Please do note that I test my code in IE8 too, so this isn't just in modern browsers. It seems to be standard, plain old javascript. So let's experiment with it. Firing up Chrome's console, I get this: ``` undeclaredVariable:{console.log('does this get logged?')} // yes it does. trueValue:{console.log('what about this?')} // same thing. falseValue:{console.log('and this?')} // same thing. ``` but then... ``` (true):{console.log('does this work too?')} // SyntaxError: Unexpected token : ``` ...and... ``` so?{console.log('is this a conditional?')}:{alert(123)} // Unexpected token . ``` So what does it do? ``` thisThing:{console.log('is used to declare a variable?')} thisThing // ReferenceError: thisThing is not defined ``` Please, I'd love it if someone could explain to me what this code is meant to do, or at least what it does.