Javascript 将图像放到画布上

我需要上传到画布上的图像，但图像一直在画布旁边，而不是里面。我做了一个代码让它发生，但不起作用。提前谢谢

Js:

不起作用的代码：

var URL = [
    "http://thumb101.shutterstock.com/display_pic_with_logo/69386/69386,1162932792,3/stock-photo-lone-car-in-four-lanes-from-above-2128171.jpg",
];
var canvas
var imgs = URL.map(function(URL) {
    var img = new Image();
    img.src = URL;
    document.body.appendChild(img);
    return img;
});

---

我使用这个代码，图像出现在画布上，然后消失。

var URL = [
    "http://thumb101.shutterstock.com/display_pic_with_logo/69386/69386,1162932792,3/stock-photo-lone-car-in-four-lanes-from-above-2128171.jpg",
];
var canvas
var imgs = URL.map(function(URL) {
    var img = new Image();
    img.src = URL;
    document.body.appendChild(img);
    return img;
});

var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d");

var background = new Image();
background.src = "http://thumb101.shutterstock.com/display_pic_with_logo/69386/69386,1162932792,3/stock-photo-lone-car-in-four-lanes-from-above-2128171.jpg";

// Make sure the image is loaded first otherwise nothing will draw.
background.onload = function(){
    ctx.drawImage(background,0,0);   
}​

var background = new Image();
background.src = "http://thumb101.shutterstock.com/display_pic_with_logo/69386/69386,1162932792,3/stock-photo-lone-car-in-four-lanes-from-above-2128171.jpg";

// Make sure the image is loaded first otherwise nothing will draw.
background.onload = function(){
    context.drawImage(background,0,0);
}