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JSON

What is it

Language independent, lightweight data-interchange format.

{
  "first_name": "John",
  "age": 27,
  "address": {
    "street_address": "21 2nd Street",
    "city": "New York",
    "state": "NY",
    "postal_code": "10021-3100"
  },
  "phone_numbers": [
    {
      "type": "home",
      "number": "212 555-1234"
    },
    {
      "type": "office",
      "number": "646 555-4567"
    }
  ],
  "spouse": null
}

JSON can be built on two structures:

  • Collection of name:value pairs
    • commonly referred to as an object, record, struct, dictionary, hash table, keyed list, or associative array.
  • Ordered list of values
    • commonly known as array, vector, list, or sequence.
// array
JSON.parse('[1,2,3]'); // [1,2,3]

// object
JSON.parse('{"1": 1,"2" :2 ,"3": 3}') // {1: 1, 2: 2, 3: 3}

JSON does not support undefined or comments.

  • JSON is not, in this sense, 1-to-1 with Javascript.

Errors

Single vs Double Quotes

JSON object should use single quotes '' to wrap records to avoid conflicting with key declaration.

Should be using double quotes "" for key representation.

Should NOT use double quotes for wrapping the JSON records

// WRONG: will throw a SyntaxError
JSON.parse("{'foo': 1}");

Trailing Commas

parse does not allow trailing commas or empty records

// trailing empty record; will throw a SyntaxError
JSON.parse('[1, 2, 3, 4, ]');

// trailling comma; will throw a SyntaxError
JSON.parse('{"foo" : 1, }');
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