Moment.js获得最后4小时的范围

Question

I am using moment.js and I would like to get the last 4 hour ranges.

Example

If it is now 26/07/2018 02:39

I would like to get an array of ranges in the of form:

[
  {from:'26/07/2018 02:00' , to:'26/07/2018 02:39'},
  {from:'26/07/2018 01:00', to:'26/07/2018 02:00'},
  {from:'26/07/2018 00:00', to:'26/07/2018 01:00'},
  {from: '25/07/2018 23:00', to:'26/07/2018 00:00'}   
] 

The above is just an example of how I am wanting to have my duration of the last 4 hours.

So far I have tried this:

let current = moment();
//here am stuck on how to substract the above

It should be something like:

moment().substract(1, 'hours') 

However, the above is subtracting one hour from 02:39 and will return 01:39 . How do I go about subtracting hours so that it will give me the desired solution?

Answer 1

You can achieve this using the .startOf() method in the momentjs library, to get your first from time.

From there, you could use the .subtract() method to decrement the times over the range that you require. Note also the use of .clone() , to ensure that the

So for example, a function like this would produce the time array that you require:

function getFourTimeRanges( timestampString ) {

    // Parse first "to" time for range, from input timestamp string 
    // (based on format in your question)
    var firstTo = moment(timestampString , 'DD-MM-YYY HH:mm');

    // Calculate first "from" time using startOf to "round down" to 
    // start of current hour
    var firstFrom = firstTo .clone().startOf('hour');

    var format = 'DD/MM/YYYY HH:mm'

    // Add first formatted range into timeRanges array    
    var timeRanges = [{ 
        from : firstFrom.format(format), 
        to : firstTo.format(format) 
    }]

    // Iterate three times to compute and add remaining time ranges
    // to timeRanges result array
    for(var i = 0; i < 3; i++) {

        // Calculate "from" and "to" times for each of the remaining 
        // times ranges we want to calculate
        var from = firstFrom.clone().subtract(i + 1, 'hours').startOf('hour')
        var to = firstFrom.clone().subtract(i, 'hours').startOf('hour')

        // Add formatted time range to timeRanges array
        timeRanges.push({ 
            from : from.format(format),
            to : to.format(format)
         })
    }

    return timeRanges
}

// Then use method as follows

getFourTimeRanges('26/07/2018 02:39')

/*
[
  {
    "from": "26/07/0018 02:00",
    "to": "26/07/0018 02:39"
  },
  {
    "from": "26/07/0018 01:00",
    "to": "26/07/0018 02:00"
  },
  {
    "from": "26/07/0018 00:00",
    "to": "26/07/0018 01:00"
  },
  {
    "from": "25/07/0018 23:00",
    "to": "26/07/0018 00:00"
  }
]
*/