
Currently I'm rewriting my [Timelinr][1] application entirely using JavaScript, thus replacing PHP which is now generating the timeline. In my code,  I have an *Event *object which looks like this:

[1]: https://veerasundar.com/timelinr/ "Timeline - create timeline online"

```javascript
    function Event(d1, d2, name) {
    	this.start = d1;
    	this.end = d2;
    	this.name = name;
    }
```

When the user adds an event to the timeline, I create a new event object and push it to an array. But it is not guaranteed that the user will add events in any chronological order. So, when the array is modified, I should make sure that the list is sorted, ordered by event start date.

JavaScript array provides an inbuilt *sort()* method. But the default functionality is limited that it sorts by converting all the elements to strings. Obviously, this sorting isn't enough for my custom object as I needed to sort the date.

The *sort()* method can accept a callback function which then determines the custom sorting order. This callback takes two parameters (a,b), compares them and finally returns a result based on the comparison.

- If it returns zero, then a and b won't be swapped (sorted as they are equal).
- It it returns less than zero, then *a *will be placed before* b *in the list.
- Otherwise, *a *will be placed after *b *in the list.

Considering that, my custom sorting function looks like this:

```javascript
    function eventSorter(a, b) {
    	if (a.start == b.start) {
    		return 0;
    	} else {
    		return a.start < b.start ? -1 : 1;
    	}
    }

    itemsArray.sort(eventSorter);
```

which will then sorts an array based on the start date.


#array (1)