Setting formatter callback using highcharts-convert.js - highcharts

Question

I am using highcharts-convert.js to create PDF charts on the serverside. I want to set the dataLabel formatter for a column chart (http://api.highcharts.com/highcharts#plotOptions.column.dataLabels). As this is a function, I can't write it in my output json file that is the input for highcharts-convert.js. So I assume I need to put it in my callback.js and call it like:
highcharts-convert.js -infile infile.js -outfile outfile.pdf -width 1000 -callback callback.js
But I can't set the formatter function in callback.js. I tried this:
function( chart ) {
var labelFormatter = function(p) {
if (this.y == 0) {
return '';
}
else {
return this.y
}
};
chart.series.dataLabels.formatter = labelFormatter;
}
But that gives me this error:
TypeError: 'undefined' is not an object (evaluating 'chart.series.dataLabels.formatter = labelFormatter')
I tried putting the formatter function outside the definition of the callback, but highcharts-convert.js won't accept that. How do I set a dataLabel formatter callback for highcharts-convert.js?

Answer 1

Well, input file for Highcharts exporting server doesn't have to be true JSON. In general, function in that JSON are supported. Just use that as example:
{"series": [{"data": [29.9, 71.5, 106.4], "dataLabels": { "enabled": true, "formatter":function(p) {if (this.y == 0) {return '';} else {return this.y+'a';}}}}]}

Answer 2

if you use callback function at serverside, Use this.
function (chart) {
options = chart.options;
var labelFormatter = function() {
if (this.y == 0) return '';
else return this.y;
}
options.yAxis[0].labels = new Object();
options.yAxis[0].labels.formatter = labelFormatter;
chart = new Highcharts.Chart(options);
chart.redraw();
}