JSFiddle - React, Tailwind, and code Playground

HTML

<canvas id="canv" width="250" height="300" style="border: 1px solid rgb(204, 204, 204); width: 400px; height: 400px; -webkit-user-select: none;"></canvas>

JavaScript

var canvas=new fabric.Canvas('canv');

var iTextSample = new fabric.IText('hello\nworld', {
  left: 50,
  top: 50,
  fontFamily: 'Helvetica',
  fill: '#333',
  lineHeight: 1.1,
  styles: {
    0: {
      0: { textDecoration: 'underline', fontSize: 80 },
      1: { textBackgroundColor: 'red' }
    },
    1: {
      0: { textBackgroundColor: 'rgba(0,255,0,0.5)' },
      4: { fontSize: 20 }
    }
  }
});

canvas.add(iTextSample);