为什么JSON.stringify搞砸了我的日期时间对象？

Question

{ id: 1533,
  story_type_id: 1,
  content_id: 470,
  created_at: Sun, 05 Feb 2012 07:02:43 GMT,
  updated_at: Sun, 05 Feb 2012 07:02:43 GMT,
  type_name: 'post' }

I have a JSON object with the "datetime" field like above. It's perfect. But when I stringify it (I want to store it in cache), I get this format:

"created_at":"2012-02-05T07:02:43.000Z"

This causes problems, because when I want to JSON.parse this, suddenly it's no longer datetime format and it's incompatible with my other format.

What can I do to solve this problem? I have 'created_at' littered everywhere throughout my application. I don't want to manually change each one.

Answer 1

It is actually possible to modify how a Date object will be serialized into JSON. Combined with the reviver function, a bi-directional solution can be created which will automatically work on serialization and can easily be used on deserialization.

First modify the serialization like this:

Date.prototype.toJSON = function() { return "{timestamp}+" . this.getTime() }

This will change the representation of a Date object into a UNIX timestamp with a prefix as a marker:

> json = JSON.stringify({test:new Date()});
"{"test":"{timestamp}1380164268633"}"

Then you can create a reviver function which will automatically filter out these values:

function json_deserialize_helper(key,value) {
  if ( typeof value === 'string' ) {
    var regexp;
    regexp = /^{timestamp}(\d*)$/.exec(value);
    if ( regexp ) {
      return new Date(+regexp[1]);
    }
  }
  return value;
}

(Credit: This code was basically copied from this answer in a related question: https://stackoverflow.com/a/14509447/2572897 )

Now with this setup, deserialization of our result from before will result in a Date object again:

> JSON.parse(json, json_deserialize_helper);
Object {test: Thu Sep 26 2013 04:57:48 GMT+0200 (CEST)}

Or you can choose not to modify the serialization but instead use the regexp to catch the standard serialization format:

function json_deserialize_helper(key,value) {
  if ( typeof value === 'string' ) {
    var regexp;
    regexp = /^\d\d\d\d-\d\d-\d\dT\d\d:\d\d:\d\d.\d\d\dZ$/.exec(value);
    if ( regexp ) {
      return new Date(value);
    }
  }
  return value;
}

Example:

> json = JSON.stringify({test:new Date()})
"{"test":"2013-09-26T03:05:26.563Z"}"
> JSON.parse(json, json_deserialize_helper)
Object {test: Thu Sep 26 2013 05:05:26 GMT+0200 (CEST)}

Answer 2

There is not special way to serialize Date objects in JSON. That's why you get the standardized string representation. You need to convert them back to Date objects by passing them to the Date constructor.

item['created_at'] = new Date(item['created_at']);

Update: With the reviver function (see comments), you can get the Date objects back.

var item = JSON.parse(row, function (key, value) {
  if (key === 'created_at') {
    return new Date(value);
  } else {
    return value;
  }
});

Answer 3

Date.prototype.toJSON = function() { return moment(this).format('L'); }

You can read more about moment documentation and tailor type of date you want to return.

Answer 4

var date = new Date();
console.log(date);//Mon Jun 11 2018 10:14:33 GMT+0430 (Iran Daylight Time)
var json = JSON.stringify(date);
console.log(json);//"2018-06-11T05:44:33.590Z"
var dateStr = JSON.parse(json);  
console.log(dateStr);//2018-06-11T05:44:33.590Z
var date = new Date(dateStr);
console.log(date);//Mon Jun 11 2018 10:14:33 GMT+0430 (Iran Daylight Time)

https://weblog.west-wind.com/posts/2014/Jan/06/JavaScript-JSON-Date-Parsing-and-real-Dates