Question

From the node REPL:

> JSON.parse('{"key" : "value"}')
{ key: 'value' }
> JSON.parse('{key : "value"}')
SyntaxError: Unexpected token ILLEGAL
    at Object.parse (native)
    at [object Context]:1:6
    at Interface.<anonymous> (repl.js:171:22)
        at Interface.emit (events.js:64:17)
    at Interface._onLine (readline.js:153:10)
    at Interface._line (readline.js:408:8)
    at Interface._ttyWrite (readline.js:585:14)
    at ReadStream.<anonymous> (readline.js:73:12)
    at ReadStream.emit (events.js:81:20)
    at ReadStream._emitKey (tty_posix.js:307:10)

Answer 1

All keys in JSON are strings, and all strings are delimited by double quotes.

JavaScript allows you to use different characters to delimit strings, and it allows you to use identifiers as keys in an object literal — but JSON is not JavaScript.