erase function is creating problem with undo button

[sanjaysamant]

I have implemented the eraser button, but getting issue while doing undo after erase. If I am erasing only one time on that time undo is working fine if I am erasing more than once then the last erased stroke works fine with undo but other are working as a line stroke.

Please see the below code

`Sketchpad.prototype._stroke = function(start, end, color, size) {
this.context.save();
if(bErasing){
this.context.globalCompositeOperation = "destination-out";
}else{
this.context.globalCompositeOperation = "source-over";
}
// if(size === 7 || size === 13){
// console.log(size)
// this.context.lineJoin = 'square';
// this.context.lineCap = 'square';
// }
// else{
this.context.lineJoin = 'round';
this.context.lineCap = 'round';
// }
this.context.strokeStyle = color;
this.context.lineWidth = size;
// switch(size){

//     case 2:
//     this.context.globalAlpha = 1;
//     break;
//     case 7:
//     this.context.globalAlpha = 0.7;
//     break;
//     case 13:
//     this.context.globalAlpha = 0.4;
//     break;
//     default:
//     this.context.globalAlpha = 0.2;
// }
this.context.beginPath();
this.context.moveTo(start.x, start.y);
this.context.lineTo(end.x, end.y);
this.context.closePath();
this.context.stroke();

this.context.restore();

};
`

and function call is here:-

` var x = "#CB7342",
y = 2;
var bErasing = false;
var canvas, canvasWidth, canvasHeight;
var ctx;
var lastPt=null;
var pathsry = [];
var points = [];
var state;
var colour;
// past states
function ySize(size) {

    y = size;
    sketchpad.penSize = y;
}
var sketchpad;
function undo(){
    bErasing = false;
    sketchpad.undo();
}

function init() {
    canvas = document.getElementById('sheet');
    ctx = canvas.getContext('2d');
    var canvasOffset = $('#sheet').offset();
    var parent = canvas.parentNode;
    canvas.width = parent.clientWidth;
    canvas.height = parent.clientHeight;
    // alert(bErasing)
    sketchpad = new Sketchpad({
        element: '#sheet',
        width: canvas.width,
        height: canvas.height,
        color: null,
        penSize: 2,
        globalAlpha: 0.1
    });
}
// function erase(){
//     sketchpad.erase();
// }
$(document).on('click', "#erase", function () {
    bErasing = true;
});

`

Please help me on this I am trying from last 3 days, but did not get resolution
Thanks