javascript - canvas.getContext ('2D' ) 返回空值

Question

我创建了一个 Canvas 并调用了它的 getContext() 方法。但它为上下文返回 null。

这是我使用的代码:

<script>
    window.onload =  init;
    function init(){
        var canvas, context;
        canvas = document.getElementById('canvas');
        context = canvas.getContext('2D');
        console.log(canvas);
        console.log(context);
    }
</script>

我在我的控制台中得到了这个:

<canvas id="canvas" width='500' height='250'>This is a canvas</canvas> null

Answer 1

我认为它是带有小写“d”的2d。以这种方式尝试:

context = canvas.getContext('2d');

如果不是那样，则根据 to the specs :

(getContext) Returns null if the given context ID is not supported, if the canvas has already been initialized with the other context type (e.g. trying to get a "2d" context after getting a "webgl" context).