Convert Result to Percentage in d3

I am just starting to learn d3.js + line chart with legend and tooltips. And I can get it to work, but I want the yAxis result to be in percentage format. Tried using tickFormat, but somehow it didn't convert my raw number to a percentage. T__T

Here is my js code

chart = d3LineWithLegend()
            .xAxis.label('Date')
            .width(700)
            .height(300)
            .yAxis.label('Frequency');


var svg = d3.select('#histogram svg').datum(data);

svg.transition().duration(1000)
  .attr('width', 700)
  .attr('height', 300)
  .call(chart);


chart.dispatch.on('showTooltip', function(e) {
    var offset = $('#histogram').offset(), // { left: 0, top: 0 }
    left = e.pos[0] + offset.left,
    top = e.pos[1] + offset.top,
    // formatter = d3.format(".04f");
    formatter = d3.format(".0%");
    var yAxis = d3.svg.axis().orient("left").tickFormat(formatter);//added this part but it didn't work
    console.log(yAxis);

    var dateObj = (new Date(e.point[0]));

    var year = dateObj.getFullYear();
    var month = dateObj.getMonth() + 1;
    var day = dateObj.getDate();
    var hours = dateObj.getHours();
    var date = month + '-' + day + '-' + year;
    if(filter === 'hour') {
      date = date + ', ' + hours + ':00';
    }

    var content = '<h3>' + date + '</h3>' +
              '<p>' +
              '<span class="value">' + (e.point[1]) + '</span>' +
              '</p>';

    nvtooltip.show([left, top], content);
});

chart.dispatch.on('hideTooltip', function(e) {
   nvtooltip.cleanup();
});

      

        
        
        
      

    

What appears to be the problem in my previous code? If I am not going to work on the client side, I am considering setting it up on the server side. But too much work.