关于javascript:学习笔记Canvas适配高清屏

有个window属性叫devicePixelRatio，能够算出过后设施的物理像素与CSS像素的比率。
语法：

value = window.devicePixelRatio;

用法：

<script>    /** @type {HTMLCanvasElement} */    let canvas = document.getElementById("canvas")    let ctx = canvas.getContext('2d')    let dpr = window.devicePixelRatio || window.webkitDevicePixelRatio || window.mozDevicePixelRatio || 1;    canvas.width = 600    canvas.height = 400    canvas.style.width = canvas.width + 'px'    canvas.style.height = canvas.height + 'px'    canvas.width = canvas.width * dpr    canvas.height = canvas.height * dpr        ctx.scale(dpr, dpr);    ctx.rect(20, 30, 400, 200)    ctx.fillStyle = "purple"    ctx.fillRect(20, 30, 400, 300)        ctx.font = '28px Arial'    ctx.fillStyle = '#fff'    ctx.fillText('ABCD', 100,150)    ctx.strokeStyle = '#fff'    ctx.strokeText('YES',100,180)      </script>