Chart.js is an awesome javascript library with an API that can handle almost any requirements. However, because Chart.js uses canvas to draw the charts, the tooltips can be frustrating. The tooltips cannot render outside of the canvas and if you have very long data, this can cause the tooltip on the chart to become useless.

Here is a very hacky workaround for putting in line breaks in your tooltips. Chart.js does not supporting rendering html inside the tooltip, so it’s not as easy as throwing in a <br>. This code will place the first line as the label and subsequent lines as the afterLabel option. afterLabel accepts an array of strings, which it will break onto new lines.

const maxTooltipLength = 50;

let wordsToArray = function(words) {
   let lines = [];
   let str = '';
   words.forEach(function (word) {
     if ((str.length + word.length + 1) <= maxTooltipLength) {
       str += word + ' ';
     } else {
       lines.push(str);
       str = word + ' ';
     }
   });
   lines.push(str);
   return lines;
}

let breakLabels = fucntion(tooltipItems, data) {
   let label = data.labels[tooltipItems.index];
   if (label.length <= maxTooltipLength) { return [ label ] }
   let words = label.split(' ');
   return wordsToArray(words);
}

let firstLabel = function (tooltipItems, data) {
  return breakLabels(tooltipItems, data)[0];
}

let otherLabels = function (tooltipItems, data) {
  return breakLabels(tooltipItems, data).slice(1);
}

let options = {
  tooltips: {
    callbacks: {
      label: firstLabel.bind(this),
      afterLabel: otherLabels.bind(this)
    }
  }
}

Binding the callback is necessary otherwise, this will the Chart instance.