Is it valid to define functions in JSON results?

Question

Part of a website's JSON response had this (... added for context):

{..., now:function(){return(new Date).getTime()}, ...}

Is adding anonymous functions to JSON valid? I would expect each time you access 'time' to return a different value.

Answer 1

Leave the quotes off...

var a = {"b":function(){alert('hello world');} };

a.b();

Answer 2

Nope, definitely not.

If you use a decent JSON serializer, it won't let you serialize a function like that. It's a valid OBJECT, but not valid JSON. Whatever that website's intent, it's not sending valid JSON.

Answer 3

The problem is that JSON as a data definition language evolved out of JSON as a JavaScript Object Notation. Since Javascript supports eval on JSON, it is legitimate to put JSON code inside JSON (in that use-case). If you're using JSON to pass data remotely, then I would say it is bad practice to put methods in the JSON because you may not have modeled your client-server interaction well. And, further, when wishing to use JSON as a data description language I would say you could get yourself into trouble by embedding methods because some JSON parsers were written with only data description in mind and may not support method definitions in the structure.

Wikipedia JSON entry makes a good case for not including methods in JSON, citing security concerns:

Unless you absolutely trust the source of the text, and you have a need to parse and accept text that is not strictly JSON compliant, you should avoid eval() and use JSON.parse() or another JSON specific parser instead. A JSON parser will recognize only JSON text and will reject other text, which could contain malevolent JavaScript. In browsers that provide native JSON support, JSON parsers are also much faster than eval. It is expected that native JSON support will be included in the next ECMAScript standard.

Answer 4

A short answer is NO...

JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others. These properties make JSON an ideal data-interchange language.

Look at the reason why:

When exchanging data between a browser and a server, the data can only be text.

JSON is text, and we can convert any JavaScript object into JSON, and send JSON to the server.

We can also convert any JSON received from the server into JavaScript objects.

This way we can work with the data as JavaScript objects, with no complicated parsing and translations.

But wait...

There is still ways to store your function, it's widely not recommended to that, but still possible:

We said, you can save a string... how about converting your function to a string then?

const data = {func: '()=>"a FUNC"'};

Then you can stringify data using JSON.stringify(data) and then using JSON.parse to parse it (if this step needed)...

And eval to execute a string function (before doing that, just let you know using eval widely not recommended):

eval(data.func)(); //return "a FUNC"

Answer 5

JSON explicitly excludes functions because it isn't meant to be a JavaScript-only data structure (despite the JS in the name).

Answer 6

No.

JSON is purely meant to be a data description language. As noted on http://www.json.org, it is a "lightweight data-interchange format." - not a programming language.

Per http://en.wikipedia.org/wiki/JSON, the "basic types" supported are:

• Number (integer, real, or floating point)
• String (double-quoted Unicode with backslash escaping)
• Boolean (true and false)
• Array (an ordered sequence of values, comma-separated and enclosed in square brackets)
• Object (collection of key:value pairs, comma-separated and enclosed in curly braces)
• null