Undo and redo command in canvas using fabric.js

Question

I want to use undo and redo command in my small website, i am using fabric.js ,anybody have any idea how to do this,following is my code.on click undo & redo button i am trying to undo & redo the object of canvas This is js fiddle link

Here is fiddle link

$(document).ready(function(){
 var canvas = new fabric.Canvas('c');
   var colorSet="red";
   $("#svg3").click(function(){
     fabric.loadSVGFromURL('http://upload.wikimedia.org/wikipedia/en/c/cd/-Islandshreyfingin.svg', function (objects, options) { 
          var shape = fabric.util.groupSVGElements(objects, options);
     shape.set({
            left: canvas.width/2,
            top: canvas.height/2,
            scaleY: canvas.height / shape.width,
            scaleX: canvas.width / shape.width
        });
       if (shape.isSameColor && shape.isSameColor() || !shape.paths) {
            shape.setFill(colorSet);
        } else if (shape.paths) {
            for (var i = 0; i < shape.paths.length; i++) {
                shape.paths[i].setFill(colorSet);
            }
        }

        canvas.add(shape);
        canvas.renderAll();
      });
     });


$("#undo").click(function(){

yourJSONString = JSON.stringify(canvas);
});
$("#redo").click(function(){
canvas.clear();
//alert(yourJSONString);
canvas.loadFromJSON(yourJSONString);
canvas.renderAll();
// alert(svgobj);
});
    });

Answer 1

var mods = 0;
//Undo Functionality
$scope.undo = function() 
{
    if (mods < $scope.state.length) {
    $rootScope.canvas.clear().renderAll();
    $rootScope.canvas.loadFromJSON($scope.state[$scope.state.length-1 - mods - 1]);         
    $rootScope.canvas.renderAll();        
    mods += 1;
    }
   }

  //Redo Functionality
    $scope.redo = function() 
    {
        if (mods > 0) {
        $rootScope.canvas.clear().renderAll();
        $rootScope.canvas.loadFromJSON($scope.state[$scope.state.length-1 - mods + 
     1]);
        $rootScope.canvas.renderAll();
        mods -= 1;
        }



}

This works fine try it!!

Answer 2

you can write your own undo and redo function using javascript and jquery like this:

// --------------------------------undo+redu--------------------------
var vall=20;
var l=0;
var flag=0;
var k=1;
var yourJSONString = new Array();
canvas.observe('object:selected', function(e) {
    //yourJSONString = JSON.stringify(canvas);
    if(k!=20)
    {
        yourJSONString[k] = JSON.stringify(canvas);
        k++;
        //$('#btn').show();
    }        
    j = k;
    var activeObject = canvas.getActiveObject();
});


$("#undo").click(function(){

  // counts the no of objects on canvas
  var objCount = canvas.getObjects().length;
  console.log("Undo"+objCount);

      if(k-1 >=0)
    {
        canvas.clear();
        canvas.loadFromJSON(yourJSONString[k-1]);
        k--;
        l++;
    }else

     {
         canvas.clear();

           k--;
           l++;
     }          
    canvas.renderAll();   

});

$("#redo").click(function(){
     // counts the no of objects on canvas
  var objCount = canvas.getObjects().length;
  console.log("redo"+objCount);

    if(l > 1)
    {
      if (objCount = 0) {
        canvas.clear();
        canvas.loadFromJSON(yourJSONString[k-1]);
        k++;
        l--;
        canvas.renderAll();

      }
      else{

        canvas.clear();
        canvas.loadFromJSON(yourJSONString[k+1]);
        k++;
        l--;
        canvas.renderAll();
      }

    }

});

This code will perform undo and redo for every change u make on canvas. It will save the state of canvas on every change and then perform undo and redo when needed.