??????????let?canvas=document.querySelector('#page2?canvas');?//獲取canvas標簽

????????????let?ctx=canvas.getContext('2d')?//獲取繪圖環(huán)境

????????????let?width=window.innerWidth;??//獲取窗口寬度

????????????let?height=window.innerHeight;?//獲取窗口高度

????????????canvas.width=width;?//繪圖高度為窗口高度

????????????canvas.height=height;//繪圖寬度為窗口寬度