Check if canvas is blank

by amaan

HTML

<canvas id='editor' style='border:solid'></canvas>

<canvas id='blank' style='display:none'></canvas>
<button id='save'>Save</button>

JavaScript

canvas = document.getElementById('editor');
ctx = canvas.getContext('2d');

canvas.addEventListener('mousemove',function(e){
    ctx.lineTo(e.pageX,e.pageY);
    ctx.stroke();
});

document.getElementById('save').addEventListener('click',function(){
    if(canvas.toDataURL() == document.getElementById('blank').toDataURL())
        alert('It is blank');
    else
        alert('Save it!');
});