<style>
    canvas {
        width: 100px;
        height: 100px;
    }   
</style>
<body>
    <canvas id="canvas1"></canvas>
    <canvas id="canvas2"></canvas>
    <script>
        function drawRect(id) {
            const canvas = document.getElementById(id);
            canvas.width = canvas.clientWidth;
            canvas.height = canvas.clientHeight;

            const ctx = canvas.getContext('2d');
            ctx.fillStyle = 'green';
            ctx.fillRect(0, 0, 100, 100);
        }

        drawRect('canvas1');
        drawRect('canvas2');
    </script>
</body>