Why is JSON.parse so picky with quotes?

Question

Basically, I am trying to create an object like this by providing a string to JSON.parse():

a = {x:1} 
// -> Object {x: 1}

Intuitively I tried:

a = JSON.parse('{x:1}')
// -> Uncaught SyntaxError: Unexpected token x

After some fiddling I figured out:

a = JSON.parse('{"x":1}')
// -> Object {x: 1}

But then I accidentally changed the syntax and bonus confusion kicked in:

a = JSON.parse("{'x':1}")
//-> Uncaught SyntaxError: Unexpected token '

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So now I am looking for an explanation why

1. one must to quote the property name
2. the implementation accepts single quotes, but fails on double quotes

Answer 1

The main reason for confusion seems to be the difference between JSON and JavaScript objects.

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JSON (JavaScript Object Notation) is a data format meant to allow data exchange in a simple format. That is the reason why there is one valid syntax only. It makes parsing much easier. You can find more information on the JSON website .

Some notes about JSON:

• Keys must be quoted with "
• Values might be strings, numbers, objects, arrays, booleans or "null"
• String values must be quoted with "

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JavaScript objects on the other hand are related to JSON (obviously), but not identical. Valid JSON is also a valid JavaScript object. The other way around, however, is not.

For example:

• keys and values can be quoted with " or '
• keys do not always have to be quoted
• values might be functions or JavaScript objects

Answer 2

As pointed out in the comments, because that's what the JSON spec specifies. The reason AFAIK is that JSON is meant to be a data interchange format (language agnostic). Many languages, even those with hash literals, do not allow unquoted strings as hash table keys.