browser market share - fixed y axis max

A line chart with the y-axis domain max fixed at 100.

The y-axis label appears at the max y value of all of the lines.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  font: 10px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.x.axis path {
  display: none;
}

.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 1.5px;
}

</style>
<body>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
<script>

var margin = {top: 20, right: 80, bottom: 30, left: 50},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var parseDate = d3.time.format("%Y-%m").parse;

var x = d3.time.scale()
    .range([0, width]);

var y = d3.scale.linear()
    .range([height, 0]);

var color = d3.scale.category10();

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom");

var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left");

var line = d3.svg.line()
    .interpolate("basis")
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.yVariable); });

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.csv("data.csv", function(error, data) {
  if (error) throw error;

color.domain(d3.keys(data[0]).filter(function(key) { return key !== "date"; }));

data.forEach(function(d) {
    d.date = parseDate(d.date);
    //console.log(d.date);
  });

// get an array of all of the values that we can 
  // compute the max of 
  var marketShares = [];
  color.domain().forEach(function(name) {
    data.map(function(d) { return +d[name] }).forEach(function(el){
      marketShares.push(el);
    })
  })

console.log("max marketShare")
  console.log(d3.max(marketShares));

console.log("marketShares");
  console.log(marketShares);

x.domain(d3.extent(data, function(d) { return d.date; }));

y.domain([
    d3.min(browsers, function(c) { return d3.min(c.values, function(v) { return v.yVariable; }); }),
    100// d3.max(browsers, function(c) { return d3.max(c.values, function(v) { return v.yVariable; }); })
  ]);

svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);

svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("x", 0) // y(d3.max(marketShares))
      .attr("y", -margin.left*.75)
      .attr("transform", "translate(0," + y(d3.max(marketShares)) + ")" + " " + "rotate(-90)")
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Market Share (%)");

console.log(d3.max(function(d) { return d.yVariable }))

var browser = svg.selectAll(".browser")
      .data(browsers)
    .enter().append("g")
      .attr("class", "browser");

browser.append("path")
      .attr("class", "line")
      .attr("d", function(d) { return line(d.values); })
      .style("stroke", function(d) { return color(d.name); });

browser.append("text")
      .datum(function(d) { return {name: d.name, value: d.values[d.values.length - 1]}; })
      .attr("transform", function(d) { return "translate(" + x(d.value.date) + "," + y(d.value.yVariable) + ")"; })
      .attr("x", 3)
      .attr("dy", ".35em")
      .style("opacity", 1)
      .text(function(d) { return d.name; });
  
});

</script>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js