strange, I always put quote marks, as I see them as totally necessary. Not in the browser, obviously, but in my mind. It helps me recording those are strings, not variables. I made too many mistakes in the likes of

    var foo = "bar";
    var baz = {
        foo: "qux"
    };

This bites especially often if you are steadily switching between JavaScript and a server-side language where that code actually does what you expect (e.g. Python).

I assume you mean you mistakenly expect baz to equal:

    {
        bar: "qux"
    }

?

Don't you use syntax highlighting? I can't imagine this ever being an issue...

Other than being idiomatic, is there any advantage to quoting or not quoting key names in JS?

Minor reasons but a) it looks untidy (to me), and b) for example if I want to change:

    foo = {
        "bar": true,
        "baz": false
    }

to:

    foo.bar = true;
    foo.baz = false;

then I have extra quotes to delete. Those half seconds add up over a year!

I guess you could argue the opposite though, that this looks messy:

    let headers = {
        Expires: 0,
        'Content-Type': 'application/json'
    }

Which leads me to believe it's a matter of personal preference, and you should just pick one and stick to it :) And look, there's even an eslint rule for it: http://eslint.org/docs/rules/quote-props

Quoted keys allows more variety in the keys (e.g. "Content-Type") but is more annoying to use if all your JS code is written in camelCase (headers["Content-Type"] vs headers.contentType).

Looks like a nice toy to play with for vim users. I already want to write a macro for it