Are all JSON objects also valid JavaScript objects?

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Update 2019: the answer is now YES as of this proposal and JavaScript versions following ECMAScript 2019 (including) will be proper supersets.

TL;DR

The answer is “no”. There are cases when JSON object won’t be valid for JavaScript. JSON is NOT a JavaScript subset.

“Little” difference

JSON

That is: due to JSON specification, you can safely use such characters, as U+2028 in any string. It is a unicode whitespace character. Not control or other special character.

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JavaScript

Well, now in JavaScript. ECMA-262 has a little difference in its definition of strings. In section 7.8.4 there is a thing, that string can contain all things except quote, a backslash or a line terminator. Now what’s line terminator? It’s in section 7.3 :

  • \u000A – Line Feed
  • \u000D – Carriage Return
  • \u2028 – Line separator
  • \u2029 – Paragraph separator

As you can see, in JavaScript symbols U+2028 and U+2029 are not allowed.

This is a sample, but since we have at least one case of difference, it’s well-enough to realize that answer is no

Image source & full description: timelessrepo

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