[Solved]-Highcharts.js draws ugly series line-Highcharts

the line is being sliced in half since it appears on the edge of the drawing "canvas".

try these yaxis options:

       yaxis: {
            tickpositions: [-3, 0, 3],
            gridlinewidth: 0,
            max: 3.1,
            endontick: false
        },

update fiddle.

for lower end, just set a min with the max value-->

yaxis: {
      tickpositions: [-3, 0, 3],
      gridlinewidth: 0,
      max: 3.1,
      min: -3.1, // i added this!
      endontick: false,
      startontick: false // and this!
},

yet another fiddle.