[Solved]-Chartjs Tooltip Line Breaks-Chart.js

This worked for me. Just simply return an array of strings as labels in tooltips.

 tooltips: {
    callbacks: {
      label: function(tooltipItem, data) {
        let label = "Line 1";
        let label2 = "Line 2";
        return [label, label2];
      }
    }
  }

At this point in time, it's not possible to add line breaks to a tooltip or axis label. Right now the developers are discussion implementation options; the discussion can be found Allow wrapping in axis labels (issue on github).

You can use tooltips footer callback,it will also not render coloured square for each list.

tooltips: {
  callbacks: {
    label: function(tooltipItem, data) {
      let label = data.datasets[tooltipItem.datasetIndex].label;
      let value = data.datasets[tooltipItem.datasetIndex].data[tooltipItem.index];
      return label + ': ' + value;
    },
    footer: function(tooltipItems, data) {
      return ['new line', 'another line'];
    }
  }
}

Actually all tool-tip callbacks support multiple lines of text, and you can use label callback as usual. It renders data label as tool-tip text by default.

Quoted from documentation:

All functions must return either a string or an array of strings. Arrays of strings are treated as multiple lines of text.

Example code:

tooltips: {
    callbacks: {
      label: (tooltipItem, data) => {
        if (tooltipItem.index % 2)
          return ['Item 1', 'Item 2', 'Item 3'];
        else
          return 'Single line';
      }
    }
  }