Originally (C) 2012 ziggy.jonsson.nyc@gmail.com
Add this script to your html and it will define d3.legend.
var svg = d3.select("body").append("svg")...
// add a data-legend attribute to your path
cities.append('path')
.attr('class', 'line')
.attr('d', line)
.attr('data-legend', 'cities')
// add legend to svg.
var legend = svg.append('g')
.attr('class', 'legend')
.attr('transform', 'translate(50, 30)')
.style('font-size', '12px')
.call(d3.legend)
Alternatively, use require with browserify:
npm install d3-legend
var d3 = require('d3');
var d3legend = require('d3-legend')(d3);