Allow changing point labels using a callback function

[etimberg]

Fixes #1110

To change the point labels, modify the config option for the scale

scale: {
    pointLabels: {
        callback: function(pointLabel, index, labels) { 
            // Return string here. String must be defined
        }
    }
}

[Jesperskate]

Hi Etimberg,

Is this fix still working? For me it isn't. I am using chartjs 2.0 (https://atmospherejs.com/jmsalash/chartjs) in Meteor:

myBarChart = new Chart(ctx, {
	    type: 'radar',
	    data: {
	      labels: labelInput,
	      datasets: [{
	          label: "Your result",
	          fill: true,
	          backgroundColor: "rgba(242,105,33,0.8)",
	          borderColor: "rgba(242,105,33,1)",
	          borderWidth: 1,
	          pointBorderWidth: 0,
	          pointRadius: 0,
	          data: dataInput
        	}]
	    },
	   	options: {
	    	scale: {
		    	pointLabels: {
		    		fontSize: 15,
		            callback: function() {
		            	var string = 'hello'
		            	console.log('hello')
		                return string
		            } 
		        },
		        ticks: {
		        	display: false,
					beginAtZero: true,
					showLabelBackdrop: false,
					stepSize: 1,
					suggestedMin: 1,
		            suggestedMax: 4,
		        },
		        gridLines: {
		            lineWidth: 4,	
		        	color: "#efefef"
		  		} 
		    },
		    layout: {
		        padding: {
		            left: 50,
		            right: 20,
		            top: 20,
		            bottom: 0
		    	}
			},
			legend:{
				display: false,
			}
	   	}
	});
}

I can change all other options of pointLabels, such as fontsize, but not the callback...

Best,

Jesper