Adding tooltip in dynamic line chart in d3.js - d3.js

Question

Can any one help me to add tool trip in line chart in d3.js
Here is what I have so far:
My Javascript:
var n = 40;
random = d3.random.normal(0, .2),
data = [-2.0236589]; // d3.range(n).map(random);
//alert(data);
var margin = {
top: 20,
right: 20,
bottom: 20,
left: 40
},
width = 960 - margin.left - margin.right,
height = 500 - margin.top - margin.bottom;
var x = d3.scale.linear()
.domain([1, n - 2])
.range([0, width]);
var y = d3.scale.linear()
.domain([-1, 1])
.range([height, 0]);
var line = d3.svg.line()
.interpolate("basis")
.x(function (d, i) {
return x(i);
})
.y(function (d, i) {
return y(d);
});
var svg = d3.select("body").append("svg")
.attr("width", width + margin.left + margin.right)
.attr("height", height + margin.top + margin.bottom)
.append("g")
.attr("transform", "translate(" + margin.left + "," + margin.top + ")");
svg.append("defs").append("clipPath")
.attr("id", "clip")
.append("rect")
.attr("width", width)
.attr("height", height);
svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + y(0) + ")")
.call(d3.svg.axis().scale(x).orient("bottom"));
svg.append("g")
.attr("class", "y axis")
.call(d3.svg.axis().scale(y).orient("left"));
var path = svg.append("g")
.attr("clip-path", "url(#clip)")
.append("path")
.datum(data)
.attr("class", "line")
.attr("d", line);
tick();
function tick() {
// alert(data);
// random();
// console.log(data);
// push a new data point onto the back
data.push(random());
//random();
// redraw the line, and slide it to the left
path.attr("d", line)
// .attr("d", valueline(data))
.attr("transform", null)
.transition()
.duration(500)
.ease("linear")
.attr("transform", function (data) {
return data.length > 40 ? "translate(" + x(0) + ",0)" : "translate(0)"
})
.each("end", tick);
// pop the old data point off the front
//alert(data.length);
if (data.length > 40) {
//alert(data.length);
data.shift();
}
}
CSS:
svg {
font: 10px sans-serif;
}
.line {
fill: none;
stroke: #000;
stroke-width: 1.5px;
}
.axis path,
.axis line {
fill: none;
stroke: #000;
shape-rendering: crispEdges;
}
JSFiddle link: http://jsfiddle.net/RajuSahoo/ug6v86cc/1/