JSON undefined value type

Question

I came across this JSON code. I noticed that it makes use of undefined value. Where can I find more information about this value type?

  tracks:[
     (         {
        codec:"h264",
        language:undefined,
        id:1,
        bitrate:785236,
        content:"video"
     }         ),
     (         {
        codec:"aac",
        language:undefined,
        id:2,
        bitrate:75969,
        content:"audio"
     }         )
  ],

Are you sure the JSON is valid? The parentheses (first noted by MuraliPrasanth) look suspicious at least. — John Dvorak
– John Dvorak, Commented Dec 10, 2012 at 7:50
That's not valid JSON. Parentheses aren't permitted. Neither is the literal undefined. undefined is a value in javascript: ecma-international.org/ecma-262/5.1/#sec-4.3.9 — David Sanders
– David Sanders, Commented Nov 6, 2014 at 22:19
are you sure that's JSON? Looks like a snippet of an object literal too me. — Brad Kent
– Brad Kent, Commented Jun 8, 2017 at 17:24
how can a defined value be undefined? in javascript, any thing is possible ;) — Rivenfall
– Rivenfall, Commented Jan 31 at 9:29

Ringo · Accepted Answer · 2021-07-04 21:56:22Z

168

undefined is not a valid JSON value, even though it is valid in javascript.

From the official JSON standard (ECMA-404, Section 5):

A JSON value can be an object, array, number, string, true, false, or null.
For JSON, use null instead of undefined: { "something": null }

edited Jul 4, 2021 at 21:56

answered Feb 18, 2013 at 22:56

Ringo

5,5333 gold badges35 silver badges52 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

totymedli Over a year ago

If you want a value to be undefined, just omit it entirely from the JSON. That way, when you try to read it after parse, it will be undefined.

Ringo Over a year ago

But that assumes you have full knowledge of what a response should look like. Which is fine if you're building both the server and client, but that is often not the case.

totymedli Over a year ago

Sure. That isn't an optimal solution, just a workaround for when you (for whatever reason) must return an undefined value.

Johan Fredrik Varen Over a year ago

Good answer, sub-optimal solution. Null and undefined are not the same. If NULL is a valid value in your system then you should be able to communicate both that "Yes, I have a value for that, and it's NULL" and "No, I don't have any value for that". PHP, e.g. suffers from its lack of undefined in its optional parameters, where it's hard (maybe even impossible?) to see whether the caller explicitly passed the default value or didn't pass a value at all. I'd say totymedli's idea is better. If the client doesn't know what to expect from a response, it's not well prepared to handle it either.

Evert Heylen Over a year ago

Note that "just omitting a value from JSON" is not possible in the case of arrays. JSON.stringify([undefined]), gives you [null], which is not a faithful representation.

|

Zombo · Accepted Answer · 2013-07-25 23:32:37Z

9

undefined is a special type where it simply indicates that the variable language is not initialized or may be it's not yet defined.

null in javascript simply indicates absence of a value, and it can also be used to indicate “no value” for numbers and strings as well as objects.The undefined value also represents absence of value, it is the value of the variables that have not been initialized and the value when you get from object property or array element that doesn’t exist undefined is a predefined global variable that is initialized to undefined value.

null and undefined doesn’t have any properties or methods.In fact, using . or [] to access property or method of these values causes a TypeError.

edited Jul 25, 2013 at 23:32

Zombo

1

answered Dec 10, 2012 at 7:40

Murali N

3,5186 gold badges30 silver badges38 bronze badges

4 Comments

John Dvorak Over a year ago

Placing a defined value into a variable makes it not undefined. The only option is that an undefined value was stored into that property or that that JSON was not generated automatically.

John Dvorak Over a year ago

language-wise, "which is undefined" binds to either the entire previous sentence (if there's a missing comma) or to "language variable", not to "data" (which is further). You have been misunderstood, I believe.

Paralife Over a year ago

although it would be useful in some cases to be able to say key:undefined in json as a method of implicit key removal when updating data stores. Many times the absence of a key is not the same thing as it having a null value

Ben Jones Over a year ago

Lol why is javascript pre-formatted

Collectives™ on Stack Overflow

JSON undefined value type

2 Answers 2

8 Comments

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

8 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related