<style>
    canvas {
        width: 100px;
        height: 100px;
    }
</style>
<script>
    function run() {
        var c = document.querySelector("canvas");
        c.width = 1;
        c.height = 1;
        var ctx = c.getContext("2d");

        var data = ctx.createImageData(1, 1);
        data.data[0] = 0xff;
        data.data[1] = 0xb4;
        data.data[2] = 0x00;
        data.data[3] = 0xa3;
        ctx.putImageData(data, 0, 0);
    }

    window.addEventListener("load", run, false);
</script>
<canvas></canvas>