checking for date range overlap

1_overlap.js

// this function takes an array of date ranges in this format:
// [{ start: Date, end: Date}]
// the array is first sorted, and then checked for any overlap

function overlap(dateRanges){
  var sortedRanges = dateRanges.sort((previous, current) => {
  
    // get the start date from previous and current
    var previousTime = previous.start.getTime();
    var currentTime = current.start.getTime();

    // if the previous is earlier than the current
    if (previousTime < currentTime) {
      return -1;
    }

    // if the previous time is the same as the current time
    if (previousTime === currentTime) {
      return 0;
    }

    // if the previous time is later than the current time
    return 1;
  });
  
  var result = sorted.reduce((result, current, idx, arr) => {
    // get the previous range
    if (idx === 0) { return result; }
    var previous = arr[idx-1];
  
    // check for any overlap
    var previousEnd = previous.end.getTime();
    var currentStart = current.start.getTime();
    var overlap = (previousEnd >= currentStart);
  
    // store the result
    if (overlap) {
      // yes, there is overlap
      result.overlap = true;
      // store the specific ranges that overlap
      result.ranges.push({
        previous: previous,
        current: current
      })
    }
   
    return result;
   
     // seed the reduce  
  }, {overlap: false, ranges: []});


  // return the final results  
  return result;
}

2_example.js

var r1 = {
  start: new Date("2/4/2001"),
  end: new Date("7/1/2002")
};

var r2 = {
  start: new Date("7/2/2002"),
  end: new Date("2/4/2003")
};

// start date overlaps with end date of previous
var r3 = {
  start: new Date("2/4/2003"),
  end: new Date("5/12/2007")
};

var ranges = [r1, r3, r2];

var output = JSON.stringify(overlap(ranges), null, 2)
console.log(output);

3_output.json

{
  "overlap": true,
  "ranges": [
    {
      "previous": {
        "start": "2002-07-02T05:00:00.000Z",
        "end": "2003-02-04T06:00:00.000Z"
      },
      "current": {
        "start": "2003-02-04T06:00:00.000Z",
        "end": "2007-05-12T05:00:00.000Z"
      }
    }
  ]
}

@Jacse agree

Yes, I also change line 26, but now work perfectly. Thx. derickbailey