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"
     }         )
  ],

Answer 1

• 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 }