@nsn,

Setting valueFormatString defines the format for labels appearing on Axis Y, which doesn’t include the negative symbol (-) incase of negative number. Instead, using labelFormatter to return an empty string should work fine in this case. Please check the below code snippet –

axisY:{
  title: "",
  tickLength: 0,
  lineThickness:0,
  margin:0,
  labelFormatter: function(e) {
     return "";
  }
},

Also, kindly take a look at this updated JSFiddle.

___________
Indranil Deo
Team CanvasJS