Marker in leaflet, click event

var map = L.map('map');
var marker = L.marker([10.496093,-66.881935]).on('click', onClick);
function onClick(e) {alert(e.latlng);}
marker.addTo(map)

When I do click in the marker, the alert message is: undefined

But if I put it in the variable map, it works! (shows latitude and longitude)

map.on('click', onClick); 

Does someone know why it doesn't work in the marker?

The accepted answer is correct. However, I needed a little bit more clarity, so in case someone else does too:

Leaflet allows events to fire on virtually anything you do on its map, in this case a marker.

So you could create a marker as suggested by the question above:

L.marker([10.496093,-66.881935]).addTo(map).on('mouseover', onClick);

Then create the onClick function:

function onClick(e) {
	alert(this.getLatLng());
}

Now anytime you mouseover that marker it will fire an alert of the current lat/long.

However, you could use 'click', 'dblclick', etc. instead of 'mouseover' and instead of alerting lat/long you can use the body of onClick to do anything else you want:

L.marker([10.496093,-66.881935]).addTo(map).on('click', function(e) {
    console.log(e.latlng);
});

Here is the documentation: https://leafletjs.com/reference.html#map-event

Here's a jsfiddle with a function call: https://jsfiddle.net/8282emwn/

var marker = new L.Marker([46.947, 7.4448]).on('click', markerOnClick).addTo(map);

function markerOnClick(e)
{
  alert("hi. you clicked the marker at " + e.latlng);
}

I found the solution:

function onClick(e) {alert(this.getLatLng());}

used the method getLatLng() of the marker

Additional relevant info: A common need is to pass the ID of the object represented by the marker to some ajax call for the purpose of fetching more info from the server.

It seems that when we do:

marker.on('click', function(e) {...

The e points to a MouseEvent, which does not let us get to the marker object. But there is a built-in this object which strangely, requires us to use this.options to get to the options object which let us pass anything we need. In the above case, we can pass some ID in an option, let's say objid then within the function above, we can get the value by invoking: this.options.objid

A little late to the party, found this while looking for an example of the marker click event. The undefined error the original poster got is because the onClick function is referred to before it's defined. Swap line 2 and 3 and it should work.