Is JavaScript Object notation proper JSON? [duplicate]

Question

If in Chrome console I run proper JSON:

{"aaa":"bbb"}

I get:

SyntaxError: Unexpected token :

If however I run e.g.:

{aaa:"bbb"}

It dosen't complain. Also running below is fine:

aaa={"aaa":"bbb"}

I thought that proper JSON must have properties names wrapped in quotation marks so why is this happening? Is JS object notation not proper JSON?

Answer 1

The problem is caused by grammar/parsing context.

Given {"aaa":"bbb"} as a program, this is a Block [statement] where "aaa" is a String followed by a colon and is thus Invalid Syntax. It can be minimally reproduced as: "aaa":"bbb", as the braces did nothing but add confusion.

Given {aaa:"bbb"} as a program, this is a statement where aaa (an Identifier) is a Label followed by the string "bbb" (also in statement context). It is fine, but it does not return an object. Likewise, it is equivalent to aaa:"bbb" in statement context.

Given aaa={"aaa":"bbb"} as a program, now the {..} is parsed in a expression context and treated as an Object Literal; the resulting object is assigned to the variable. An expression context can be forced with other grammar constructs, such as +{"aaa":"bbb"}, ({"aaa":"bbb"}) or, more usefully, console.log({"aaa":"bbb"}).

With all that out of the way, because the JavaScript Object Literal syntax simply didn't apply in two out of the three cases:

JSON is almost-but-not-quite a proper-subset of JavaScript Object Literals; use proper JSON tooling and validation.