//http://stackoverflow.com/q/33728173/371899

var createTestCase = function (inputNumber, expectedOutput) {

      return Object.create({}, {

        inputNumber: { value: inputNumber, enumerable: true },

        expectedOutput: { value: expectedOutput, enumerable: true }

      });

      },

    testCaseList = [

      createTestCase(16,0),

      createTestCase(17,10),

      createTestCase(18,20),

      createTestCase(19,30),

      createTestCase(20,40),

      createTestCase(21,50),

      createTestCase(6,60),

      createTestCase(7,70),

      createTestCase(8,80),

      createTestCase(9,90),

      createTestCase(10,100)

    ],

    svg = d3.select("svg"),

    group = svg.append("g"),

    width = 250,

    height = 250,

    domain1 = [16, 21],

    domain2 = [6, 10],

    range = [0, 100],

    midPoint = [50, 60],

    data = [16,17,18,19,20,21,6,7,8,9,10],

    scaleX = d3.scale.linear().domain([6,21]).range([30, width]),

    scaleY = d3.scale.linear().domain([10, 100]).range([height, 30]),

    circle = group.selectAll("circle").data(data),

    circleEnter = circle.enter(),

    addCircles = circleEnter.append("circle").attr({

      cx: scaleX,

      cy: function (d) { return scaleY(multiScale(d, domain1, domain2, range, midPoint));},

      r: 14,

      stroke: "#000",

      "stroke-width": "2px",

      "fill": "#0f0"

    }),

    addText = group.selectAll("text").data(data).enter().append("text").text(function (d) {

      return "" + d + " . scales to " + multiScale(d, domain1, domain2, range, midPoint);

    }).attr({x: scaleX, y:function (d) { return scaleY(multiScale(d, domain1, domain2, range, midPoint));},

            //"text-anchor": "middle",

            "alignment-baseline": "middle",

            dx: function (d) { return d<10 ? -5 : -9; }, dy: 2});

​

function multiScale(inputNumber, domain1, domain2, range, midPoint) {

  var scale1 = d3.scale.linear().domain(domain1).range([range[0],midPoint[0]]),

      scale2 = d3.scale.linear().domain(domain2).range([midPoint[1], range[1]]);

  return (domain1[0] <= inputNumber && inputNumber <= domain1[1]) ? scale1(inputNumber)  : scale2(inputNumber);

}

​

function runTestCases(sut, testCaseList) {

  testCaseList.forEach(function (testCase) {

    var actualOutput = sut.scale(testCase.inputNumber, domain1, domain2, range, midPoint),

        because = JSON.stringify(testCase) + ", actualOutput: " + actualOutput;

    console.log(actualOutput === testCase.expectedOutput ? "pass" : "fail: " + because);

  });

}

​

runTestCases({scale: multiScale}, testCaseList);

​

console.log("end.");