JSON Datetime Between Python and JavaScript

How to work with datetimes betwixt javascript, JSON, and python, and mongodb?

There are obviously a lot of requirements to consider when dealing with time. However, in the case you want to maintain a Date/Time to be displayed to user in their time zone and use mongo/python/java/javascript, I've used ISO 8601 date formats and always store UTC (Zulu) time. Also, if you truly want to maintain the actual time that something occured, not only do you need to store the "date/time" you need to also store the "timezone" (for example IANA timezone string) where the event occurred.

For a lifetime a reading, you can search for "date time best practices". This answer has a good start on discussion: Daylight saving time and time zone best practices

Alright, now to the code (all of this can be found readily on the internet if you search for
" parse||output ISO 8601 parsing" (e.g. "python parse ISO 8601 date string"):

1. JSON - on the wire between JavaScript and Python backend send a complex (can be simple if you have no need to preserve time zone) object with ISO-8601 formatted string and string to store time zone string:
   
   
{
"dateTime": "1970-07-10T12:00:00.047Z",
"timeZone": "America/New_York"
}


2. Java Script

   a. read datetime string JavaScript: Which browsers support parsing of ISO-8601 Date String with Date.parse
   
   
var d = Date.parse("2011-04-26T13:16:50Z");

   b. write datetime string How do I output an ISO 8601 formatted string in JavaScript?
   
   
var date = new Date();
date.toISOString(); //"2011-12-19T15:28:46.493Z"


3. Python

   a. read datetime string How do I translate a ISO 8601 datetime string into a Python datetime object?
   
   
import dateutil.parser
yourdate = dateutil.parser.parse(datestring)

   b. write datetime string Python - Convert date to ISO 8601
   
   
import dateutil.parser as parser
date.isoformat()


4. Mongo - store datetime as native datetime field http://docs.mongodb.org/manual/reference/mongodb-extended-json/#date
   
   a. store datetime string (notice "$date" and that datetime is in ZULU/UTC (denoted by 'Z')):
   
   
"dateTime" : { "$date" : "1970-07-10T13:00:00.047Z"}


Reference:

1. IANA TimeZone Databasehttp://en.wikipedia.org/wiki/Tz_database

2. The google calendar API (event resource) can be used as an example for RFC 3339, as well (see start/end): https://developers.google.com/google-apps/calendar/v3/reference/events

json date and javascript date and finding the difference in days

First i would have a variable to convert the JSON obj date to date format by simply passing it as a string

var creationDate = new Date(this.creatorobject.creationdate);

ex : const d = new Date("2015-03-25");

then next find the difference between the 2 days ie: today - creationDate..

If they are 2 date formats then you get milliseconds. Convert milliSeconds to days and round it up to get a date.

var today = new Date();
var creationDate = new Date("2022-01-01");
var diff = today - creationDate;
const convertedDate = diff / (1000*60*60*24);
console.log(convertedDate);

How to overcome datetime.datetime not JSON serializable?

Updated for 2018

The original answer accommodated the way MongoDB "date" fields were represented as:

{"$date": 1506816000000}

If you want a generic Python solution for serializing datetime to json, check out @jjmontes' answer for a quick solution which requires no dependencies.

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As you are using mongoengine (per comments) and pymongo is a dependency, pymongo has built-in utilities to help with json serialization:

http://api.mongodb.org/python/1.10.1/api/bson/json_util.html

Example usage (serialization):

from bson import json_util
import json

json.dumps(anObject, default=json_util.default)

Example usage (deserialization):

json.loads(aJsonString, object_hook=json_util.object_hook)

---

Django

Django provides a native DjangoJSONEncoder serializer that deals with this kind of properly.

See https://docs.djangoproject.com/en/dev/topics/serialization/#djangojsonencoder

from django.core.serializers.json import DjangoJSONEncoder

return json.dumps(
  item,
  sort_keys=True,
  indent=1,
  cls=DjangoJSONEncoder
)

One difference I've noticed between DjangoJSONEncoder and using a custom default like this:

import datetime
import json

def default(o):
    if isinstance(o, (datetime.date, datetime.datetime)):
        return o.isoformat()

return json.dumps(
  item,
  sort_keys=True,
  indent=1,
  default=default
)

Is that Django strips a bit of the data:

 "last_login": "2018-08-03T10:51:42.990", # DjangoJSONEncoder 
 "last_login": "2018-08-03T10:51:42.990239", # default

So, you may need to be careful about that in some cases.

What is the right JSON date format?

JSON itself does not specify how dates should be represented, but JavaScript does.

You should use the format emitted by Date's toJSON method:

2012-04-23T18:25:43.511Z

Here's why:

1. It's human readable but also succinct

2. It sorts correctly

3. It includes fractional seconds, which can help re-establish chronology

4. It conforms to ISO 8601

5. ISO 8601 has been well-established internationally for more than a decade

6. ISO 8601 is endorsed by W3C, RFC3339, and XKCD

That being said, every date library ever written can understand "milliseconds since 1970". So for easy portability, ThiefMaster is right.

Is it possible to write date as DateTime format in JSON using Python without converting it to string

Simple answer is No, JSON does not have a native datetime representation, so it will appear as a string; however, if you use a standard that is agreed upon, the receiving application can parse the variable into a datetime object, if they choose to. If you do not know what format they may agree with, I would recommend just making it a standard ISO 8601(Combined date and time in UTC), that way it can be parsed by the receiver, and retain the correct value regardless of time zone.

Use JSON to communicate between Python and JavaScript to change CSS of a Website

Because jsondata is defined within the definition of the callback function request.onload while you are trying to access it outside the code block. You may want to move console.log inside the onload function.

request.onload = function() {
    var data = request.response;
    var jsondata = JSON.parse(data);
    return jsondata;
}

console.log(jsondata['text_06']); // jsondata is not accessible

It's also recommended that request.send() is called after having request.onload defined

request.onload = function() {
    var data = request.response;
    var jsondata = JSON.parse(data);
    console.log(jsondata['text_06']);
    return jsondata;
    }
request.send();

If you want to access jsondata outside, you may want to define a global variable outside the onload function and update it once you receive the data.

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