I am currently working on a Flot graph, the API which seems pretty powerful overall, although examples of advanced use are not widely documented.
The API suggests there
The link in Simon's answer worked very well to provide a hook to use with the floating tooltips. However, I found that I had to dig around and cut code up in order to accomplish the hover affect. Here is the result (basically verbatim from http://people.iola.dk/olau/flot/examples/interacting.html).
The only setting that needs to change in the flot initialization is in the options object. It needs to include this as one of the options:
var options = {
//... : {},
grid: { hoverable: true }
};
This function constructs and shows the tooltip element when called. The parameters x and y are offsets inside of the flot so the tooltip positions properly. The contents are what are shown in the tooltip
function showTooltip(x, y, contents) {
$('<div id="tooltip">' + contents + '</div>').css({
position: 'absolute',
display: 'none',
top: y + 5,
left: x + 5,
border: '1px solid #fdd',
padding: '2px',
'background-color': '#fee'
}).appendTo("body").fadeIn(200);
}
This is the bind, it should only be called once when the element used as a placeholder for flot is available. It wires the event handler. previousPoint is used as a flag for displaying the tooltip
var previousPoint = null;
$("#flotPlaceHolder").bind("plothover", function (event, pos, item) {
if (item) {
if (previousPoint != item.dataIndex) {
previousPoint = item.dataIndex;
$("#tooltip").remove();
var x = item.datapoint[0].toFixed(0),
y = item.datapoint[1].toFixed(0);
showTooltip(item.pageX, item.pageY, "(" + x + "," + y + ")");
}
}
else {
$("#tooltip").remove();
previousPoint = null;
}
});
You can add custom data to the data array and use that to display tooltips.
See my answer and full example here: displaying custom tooltip when hovering over a point in flot
http://data.worldbank.org is built using Flot and uses tooltips.
http://craigsworks.com/projects/qtip2/demos/#flot is my favorite JS tooltip library. Its pretty badass and has flot integration.
Have a look at this flot example which demonstrates tooltips for plot points on the chart. (Make sure you select the Enable tooltip checkbox.)
Check out this library for tooltip and flot integration
https://github.com/krzysu/flot.tooltip