var margin = {top: 20, right: 100, bottom: 30, left: 100},

    width = 960 - margin.left - margin.right,

    height = 500 - margin.top - margin.bottom;

​

var xScale = d3.scale.linear()

    .domain([0, 20])

    .range([0, width]);

​

var yScale = d3.scale.linear()

    .domain([0, 20])

    .range([height, 0]);

​

var xAxis = d3.svg.axis()

    .scale(xScale)

    .orient("bottom");

​

var yAxis = d3.svg.axis()

    .scale(yScale)

    .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 + ")");

​

svg.append('g')

    .attr('class', 'x axis')

    .attr("transform", "translate(0," + height + ")")

    .call(xAxis);

​

svg.append('g')

    .attr('class', 'y axis')

    .call(yAxis);

​

var trianglePoints = xScale(3) + ' ' + yScale(18) + ', ' + xScale(1) + ' ' + yScale(0) + ', ' + xScale(12) + ' ' + yScale(3) + ' ' + xScale(12) + ', ' + yScale(3) + ' ' + xScale(3) + ' ' + yScale(18);

​

console.log(trianglePoints);

​

svg.append('path')

    .attr('d', function(d) { 

        var x = xScale(3), y = yScale(18);

        return 'M ' + x +' '+ y + ' l ' + xScale(10) + ' ' + yScale(10) + ' l ' + -xScale(10) + ' 0 z';

      })

    .style('stroke', 'blue');