Edit in JSFiddle

window.onload = function () {
    
    //create paper
    var paper = Raphael("canvas");
    paper.rect(0,0,1000,1000);
    
}

<div id="canvas">ここはどこ？わたしはだあれ？</div>

body,html
{
    height:100%;
    margin:0;
}

#canvas 
{
    height:99%;
    background:#aaa;
}