javascript - How to edit a FabricJS IText and apply new styles (e.g. highlighting, etc...)

Question

I want to edit the highlighted characters in a text in canvas using fabric.js, like change its color, font, style etc.

just like this http://fabricjs.com/test/misc/itext.html

to @user43250937 hey uhm. I tried it and it works! :D thanks. I tried Underline, Bold, Italic, but I have a problem changing the color of the text, I tried :

// "cinput" is the id of the color picker.


addHandler('cinput', function(obj) {
    var color =  $("#cinput").val();

    var isColor = (getStyle(obj, 'fill') || '').indexOf(color) > -1;

     setStyle(obj, 'fill', isColor ? '' : color);

});

Answer 1

Usually answers without a description of what you tried and what didn't work are completely ignored here, i'm answering this time because the fabricjs library is quite complex and the documentation is a bit lacking sometimes...

That page has samples for the IText object, text that can be edited in place (the content of the basic fabricjs text object can be modified only from outside via javascript).

Building a static IText object with different styles applied it's simple:

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
world', {
  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);

Link to JSFiddle

As you can see you just specify the style for every character of each for each line (first for the hello line, then for the world line).

If you want something dynamic with the ability to select some text and change the appearance/style there is some work to do, you'll need to:

1. Add a button or a clickable element for each style (bold,italic,change color, change background,etc...) that you want to apply dynamically;
2. Add a click listener to each button with some code that changes the style of the selected text inside the IText.

You'll need a basic function that add handlers that you will reuse for every style button:

function addHandler(id, fn, eventName) {
  document.getElementById(id)[eventName || 'onclick'] = function() {
    var el = this;
    if (obj = canvas.getActiveObject()) {
      fn.call(el, obj);
      canvas.renderAll();
    }
  };
}

And some helper functions to change the styles:

function setStyle(object, styleName, value) {
  if (object.setSelectionStyles && object.isEditing) {
    var style = { };
    style[styleName] = value;
    object.setSelectionStyles(style);
  }
  else {
    object[styleName] = value;
  }
}

function getStyle(object, styleName) {
  return (object.getSelectionStyles && object.isEditing)
    ? object.getSelectionStyles()[styleName]
    : object[styleName];
}


addHandler('underline', function(obj) {
  var isUnderline = (getStyle(obj, 'textDecoration') || '').indexOf('underline') > -1;
  setStyle(obj, 'textDecoration', isUnderline ? '' : 'underline');
});

Link to working JSFiddle with a working underline button.

A bit of coding is involved as you can see, but it's not that complex, for the full list of available style options you can check the fabricjs documentation.