How to customize the tooltip of a Chart.js 2.0 Doughnut Chart?

I'm trying to show some data using a doughnut chart from Chart.js2.

My current chart looks like this:

My desired output must show another attribute, which is the percentage, and looks like this:

I've read the documentation, but I can't cope with this because it's very general and I'm new to JavaScript.

My code for the first chart is the following:

const renderCashCurrencyPie = (cashAnalysisBalances) => {
  if (cashAnalysisBalances) {
    const currenciesName = cashAnalysisBalances
    .map(curName => curName.currency);

    const availableCash = cashAnalysisBalances
    .map(avCash => avCash.availableCash);

    let currenciesCounter = 0;
    for (let i = 0; i < currenciesName.length; i += 1) {
      if (currenciesName[i] !== currenciesName[i + 1]) {
        currenciesCounter += 1;
      }
    }

    const currenciesData = {
      labels: currenciesName,
      datasets: [{
        data: availableCash,
        backgroundColor: [
          '#129CFF',
          '#0C6DB3',
          '#FF6384',
          '#00FFFF'
        ],
        hoverBackgroundColor: [
          '#FF6384',
          '#36A2EB',
          '#FFCE56',
          '#00FFFF'
        ]
      }]
    };

You can customize the tooltips using the chart options tooltip configuration section, as explained here: http://www.chartjs.org/docs/latest/configuration/tooltip.html#tooltip-configuration

As shown in the example code below, you can change things like color, sizing and styles. Check out the documentation linked above for a full list of configurable options.

If you want to add the percentage to the tooltip display, you can use tooltip callbacks. The documentation has a list of all the possible customizable callback fields.

In the below example, I set the "title" to show the label name, "label" to show the value, and added the percentage to "afterLabel".

var myChart = new Chart(ctx, {
  type: 'doughnut',
  data: data,
  options: {
    tooltips: {
      callbacks: {
        title: function(tooltipItem, data) {
          return data['labels'][tooltipItem[0]['index']];
        },
        label: function(tooltipItem, data) {
          return data['datasets'][0]['data'][tooltipItem['index']];
        },
        afterLabel: function(tooltipItem, data) {
          var dataset = data['datasets'][0];
          var percent = Math.round((dataset['data'][tooltipItem['index']] / dataset["_meta"][0]['total']) * 100)
          return '(' + percent + '%)';
        }
      },
      backgroundColor: '#FFF',
      titleFontSize: 16,
      titleFontColor: '#0066ff',
      bodyFontColor: '#000',
      bodyFontSize: 14,
      displayColors: false
    }
  }
});

Working JSFiddle: https://jsfiddle.net/m7s43hrs/