Formatter Function

To use a simple formatter function (e.g. formatter in tooltip, data_labels, and labels), you can add functionable-json to your Gemfile and use it like so:

<%= area_chart series, tooltip: {y: {formatter: function(val) { return '$' + parseFloat(val).toLocaleString() }}} %>

Or, without the functionable-json gem, use function as object as follows:

<%= area_chart series, tooltip: {y: {formatter: {function: {args: "val", body: "return '$' + parseFloat(val).toLocaleString();"}} }} %>