history-when

history-when is a set of Date based filters that apply to array of dated objects. For instance, it is possible to keep all objects whose date correspond to today, or yesterday. It is also possible to keep one object per hour.

It has been designed for history-trend, but it can be used independently. It has been inspired by Ramda.

Installation

To use with node:

$ npm install history-when

Usage

W.last24h

Retains dated objects whose date is no older than 24 hours ago.

Let us consider present to be 2015-12-17T13:24:00

var W = require('history-when')({fixedPresent: new Date('2015-12-17T13:24:00')}),
    objects = [
        {date: new Date('2015-12-17T19:24:00'), name: 'after present'},
        {date: new Date('2015-12-17T13:24:00'), name: 'present' },
        {date: new Date('2015-12-17T13:23:59'), name: 'one second before present'},
        {date: new Date('2015-12-16T13:24:00'), name: '24 hours before present'}
    ];

// issuing
W.last24h(objects);

// returns
[
    {date: new Date('2015-12-17T13:24:00'), name: 'present' },
    {date: new Date('2015-12-17T13:23:59'), name: 'one second before present'}
]

W.lastWeek

Retains dated objects whose date is no older than 7 days ago.

W.hourly

Retains one object per hour.

W.daily

Retains one object per day.

W.today

Retains all objects whose date is today.

W.skipWeekend

Filters out object dated on Saturday or Sunday.

And combination

It is possible to combine several filters, using W.and function.

 var W = require('history-when')({fixedPresent: new Date('2015-11-23T12:04:00')}),
            objects = [
                {date: new Date('2015-11-17T11:10:00')},
                {date: new Date('2015-11-18T11:01:00')},
                {date: new Date('2015-11-19T11:02:00')},
                {date: new Date('2015-11-20T11:20:00')},
                {date: new Date('2015-11-21T11:03:00')},
                {date: new Date('2015-11-22T22:30:00')},
                {date: new Date('2015-11-23T11:04:00')}
            ];
// issuing
W.and(W.skipWeekend, W.last24h)(objects);

// returns
[{date: new Date('2015-11-23T11:04:00')}]

Configuring Present

By default, present is Date.now() each time a filter is invoked.

It is possible to fix present by specifying present date of your choice :

var W = require('history-when')({fixedPresent: new Date('1995-12-17T10:24:00')});

Date objects

By default, date of object are accessed by object.date. It is possible to change date access by passing a getter:

var getter = function(o) {return o.creationdate},
    W = require('history-when')({date: getter)});