# JSON encoding with records and 'null'/'undefined' mapping
Originally, this was a wrapper around `jsx` to handle encoding and decoding of Erlang records, but [euneus](https://github.com/williamthome/euneus) gives to
jsxrecord a better performance.
## JSON null handling
To ease the interop between Erlang and JSON the 'null' handling is changed:
Erlang -> JSON -> Erlang
undefined null undefined
null null undefined
## How to use
Before records can be encoded or decoded the record definitions need to be loaded.
After the definitions are loaded then all encoding/decoding is done transparently.
### Loading record definitions
The record definitions are loaded from modules and compiled into a runtime loaded module
containing all field names and default values.
To add record definitions from `mymodule`
ok = jsxrecord:load_records( [ mymodule ]).
To see the current record definitions:
jsxrecord:record_defs()
This returns a map with all known record definitions.
### Encoding/decoding records
Let's assume the following record definition has been loaded:
-record(test, { a = 1, b = 2, c }).
This can now be encoded with:
jsxrecord:encode( #test{} ).
The resulting JSON is:
{"_record":"test","a":1,"b":2,"c":null}
Decoding returns the `#test{}`:
#test{} = jsxrecord:decode(<<"{\"_record\":\"test\",\"a\":1,\"b\":2,\"c\":null}">>).
Defaults are automatically added for fields missing in the JSON:
#test{ a = 1, b = 2, c = undefined } = jsxrecord:decode(<<"{\"_record\":\"test\"}">>).
### Encoding and decoding datetime and timestamp tuples
Datetime tuples are assumed to be in UTC, and are converted into an ISO8601 string:
<<"\"2008-12-10T13:30:00Z\"">> = jsxrecord:encode({{2008, 12, 10}, {13, 30, 0}})
They are converted back into a datetime tuple:
{{2008, 12, 10}, {13, 30, 0}} = jsxrecord:decode(<<"\"2008-12-10T13:30:00Z\"">>)
Erlang timestamp tuples are also converted into an ISO8601 string, but with added precision:
<<"\"2020-06-12T14:00:11.571Z\"">> = jsxrecord:encode({1591,970411,571321})
A little bit of precision is lost when converting it back to a timestamp tuple:
{1591,970411,571000} = jsxrecord:decode(<<"\"2020-06-12T14:00:11.571Z\"">>)
## Configuration
Set the application env `jsxrecord.record_modules` to a list of modules whose records need to
be loaded on first use of the encoder or decoder.
## Performance
The input of encode and the output of decode are parsed and expanded.
This makes the encoder and decoder slower than pure `jsx`.
Though the difference shouldn't be too bad in normal usage.
