Links

• JSON
  • stringify(value[, replacer [, space]])
    • replacer parameter
    • toJSON()
      • If an object being stringified has a property named toJSON of type Function, then the return value from toJSON() is serialized instead of the object itself.
    • Note: toJSON is used before the object is passed to the replacer. This can be an issue for Date objects. See this StackOverflow thread.
  • parse(text[, reviver])
    • reviver parameter

On JSON.stringify

Ref:  stringify(value[, replacer [, space]])

• Properties are stringified in arbitrary order.
• Non-primitive objects with primitive equivalents are serialized as primitives.  (e.g. Boolean, Number and String)
• If undefined, a function, or an XML value is encountered during conversion it is either omitted (when it is found in an object) or censored to null (when it is found in an array).

Example:

JSON.stringify({
    foo: function() {},
    arr: [function bar() {}, undefined, new String("strobj")]
});

Output

{"arr":[null,null,"strobj"]}

replacer parameter to JSON.stringify

Refer MDN: replacer parameter

The replacer parameter is either a function OR an array. As a function, it has the properties:

• Parameters
  • key: object in which the "key" was found.
  • value: value of that key in the object.
• this: set to the object from which "key" and "value" have been pulled.
• First call: In the very first call, key is the empty string and this is the original object passed to JSON.stringify.
• Return value
  • string: this string is used as the property's value instead of the original value.
  • number or bool: the string corresponding to the number, or "true"/"false" for bool, is used as the property's value.
  • undefined OR Function: this key/value is skipped.
  • something else: recursively stringify this object instead of the original value (using this same replacer.)
• Note: You can't use the replacer function to remove values from an array. null is used if you return undefined or Function from the replacer.

reviver parameter to JSON.parse

Refer MDN: reviver parameter

The parsed JS object and all it's properties are recursively (starting from the most nested) transformed using the reviver to reconstruct the final object.

• Parameters
  • key: property name
  • value: property value
• this: object containing that key and value.
• Last call: In the final call, key is set to the empty string. The result of this call is the final result of JSON.parse so you must handle this case.
• Return value: If undefined, then that property is skipped. Else, the result is used as the value instead.

Sample reviver snippet

function _prefixAllKeys(obj, prefix) {
  if (obj instanceof Object && Object.getPrototypeOf(obj) === Object.prototype) {
    var result = {};
    for (var k of Object.keys(obj)) {
      result[prefix + k] = obj[k];
    }
    return result;
  } else {
    return obj;
  }
}

function jsonReviver(key, obj) {
  return _prefixAllKeys(obj, "ckck_");
}

var o1 = {
  a: [1, 2],
  b: { c: 1}
};

var json = JSON.stringify(o1);

// logs: { ckck_a: [ 1, 2 ], ckck_b: { ckck_c: 1 } }
console.log(JSON.parse(json, jsonReviver));