Value Goals

var decimal_data = [];
for (var x = 0; x <= 360; x += 10) {
  decimal_data.push({
    x: x,
    y: Math.sin(Math.PI * x / 180).toFixed(4)
  });
}
window.m = Morris.Line({
  element: 'graph',
  data: decimal_data,
  xkey: 'x',
  ykeys: ['y'],
  labels: ['sin(x)'],
  parseTime: false,
  goals: [-1, 0, 1]
});