extend x and y axis length in scatterplot, d3js - d3.js

Question

I am trying to extend the x and y axis length and add the arrow at the end. Here is my code and plunker. I need x axis to extend beyond 4.6 and y-axis beyond "AS" and add an arrow at the end. Kindly help.
https://plnkr.co/edit/tA6oyKQCCmhNadbARR89?p=preview
var margin = {top: 20, right: 20, bottom: 20, left: 40},
width = 420 - margin.left - margin.right,
height = 500 - margin.top - margin.bottom;
var x = d3.scale.linear()
.range([0, width]);
var y = d3.scale.ordinal().rangePoints([height, 0])
var color = d3.scale.category10();
var xAxis = d3.svg.axis()
.scale(x)
.orient("bottom").outerTickSize(0);
var yAxis = d3.svg.axis()
.scale(y).tickSize(-width).outerTickSize(0)
.orient("left");
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 + ")");
d3.tsv("data.tsv", function(error, data) {
if (error) throw error;
data.forEach(function(d) {
d.sepalWidth = +d.sepalWidth;
});
x.domain(d3.extent(data, function(d) { return d.sepalWidth; })).nice();
y.domain(data.map(function(d) { return d.sepalLength;}));
svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + (height) + ")")
.call(xAxis);
svg.append("g")
.attr("class", "y axis")
.call(yAxis);
svg.selectAll(".dot")
.data(data)
.enter().append("circle")
.attr("class", "dot")
.attr("r", 3.5)
.attr("cx", function(d) { return x(d.sepalWidth); })
.attr("cy", function(d) { return y(d.sepalLength); })
.style("fill", function(d) { return color(d.species); });
var legend = svg.selectAll(".legend")
.data(color.domain())
.enter().append("g")
.attr("class", "legend")
.attr("transform", function(d, i) { return "translate(0," + i * 20 + ")"; });
legend.append("text")
.attr("x", width - 24)
.attr("y", 9)
.attr("dy", ".35em")
.style("text-anchor", "end")
.text(function(d) { return d; });
});

Answer 1

Easiest way is to just tack on a custom path to the end of the axis:
svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + (height) + ")")
.call(xAxis)
.append("path")
// add extension arrow
.attr("d", "M" + width + ",0L" + (width + 20) + ",0L" + (width + 20) + ",-5L" + (width + 30) + ",0L" + (width + 20) + ",5L" + (width + 20) + ",0L");
svg.append("g")
.attr("class", "y axis")
.call(yAxis)
.append("path")
// add extension arrow
.attr("d", "M0,0L0,-20L-5,-20L0,-30L5,-20,L0,-20Z");
Updated plunker.