javascript - Is '""' a valid JSON string? - Stack Overflow

admin管理员组

文章数量:1297014

I am confused. To quote json

JSON is built on two structures:

• A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
• An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.

So, I don't think '""' should be a valid JSON string as its neither a list values(i.e. does not start with '[' and ends with ']') but JSON.parse doesn't give exception and returns empty string.

Is it a valid JSON string.

I am confused. To quote json

JSON is built on two structures:

• A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
• An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.

So, I don't think '""' should be a valid JSON string as its neither a list values(i.e. does not start with '[' and ends with ']') but JSON.parse doesn't give exception and returns empty string.

Is it a valid JSON string.

• javascript
• json

Share Improve this question Follow asked Mar 10, 2013 at 17:57 Hariom BalharaHariom Balhara 89299 silver badges1919 bronze badges 2

• When I try JSON.parse(""), I get: SyntaxError: Unexpected end of input. However, JSON.parse('{"x": ""}') parses fine. – Ted Hopp Commented Mar 10, 2013 at 18:05
• 1 you need to run JSON.parse('""') – Hariom Balhara Commented Mar 10, 2013 at 18:14

Add a ment  | 

4 Answers 4

Sorted by: Reset to default 5

So, I don't think "" should be a valid JSON string

It is a valid JSON string (which is a data type that may appear in a JSON text).

as its neither a list values(i.e. does not start with '[' and ends with ']')

A JSON text (i.e. a plete JSON document) must (at the outermost level) be…

(Here I cut the original answer because the specification has been revised).

A JSON text is a serialized value.

(quoting the JSON specification

So "" is a valid JSON text. This wasn’t the case when the original version of this answer was written. Some JSON parsers may break when the outer most value is not an object or array.

---

The original answer (which is now incorrect resumes here):

…either an object or an array. A string is not a valid JSON text.

The formal specification says:

A JSON text is a serialized object or array.

But back to quoting the question here:

but JSON.parse doesn't give exception and returns empty string.

The JSON parser you are using is being overly-liberal. Don't assume that all JSON parsers will be.

For example, if I run perl -MJSON -E'say decode_json(q{""})' I get:

JSON text must be an object or array (but found number, string, true, false or null, use allow_nonref to allow this) at -e line 1.

No, '' is not valid JSON. JSON.parse('') does throw an error – just look in your browser console.

Next time you have an "is this valid JSON?" question, just run it through a JSON validator. That's why they exist.

Following the newest JSON RFC 7159, "" is in fact valid JSON. But in some earlier standards it wasn't.

Quote:

A JSON text is a sequence of tokens. The set of tokens includes six structural characters, strings, numbers, and three literal names.

A JSON text is a serialized value. Note that certain previous specifications of JSON constrained a JSON text to be an object or an array. Implementations that generate only objects or arrays where a JSON text is called for will be interoperable in the sense that all implementations will accept these as conforming JSON texts.

2023 Update

The other answers on this question are outdated and contain some incorrect information. The most recent JSON specification is RFC 8259, which obsoletes the previous RFCs referenced here. It says:

Note that certain previous specifications of JSON constrained a JSON text to be an object or an array.

A string by itself is therefore valid as an entire JSON text. It doesn't need to be contained within an outer object construct. The examples section of the RFC shows this:

Here are three small JSON texts containing only values:

"Hello world!"

42

true

The content of the string of course is irrelevant, so an empty string by itself is acceptable.

Note: JSON requires that strings be quoted with " so single quotes are still not valid:

""    // Valid
''    // Invalid

本文标签： javascriptIs 39quotquot39 a valid JSON stringStack Overflow