做园区巡检需求时，需要巡检打卡拍照上传功能，并且在照片上添加当前时间的水印

1. 创建canvas
2. 拍照后拿着图片画到canvas上
3. 同时获取当前时间也画到canvas上，
4. 再将canvas生成base64的url
5. 拿着合成的图片url进行下面的逻辑
6. 上代码

function addWatermark(imagePath,mark,calback) {
	let date = new Date();
	let year = date.getFullYear();
	let month = date.getMonth() + 1;
	let day = date.getDay();
	let hours = date.getHours();
	let minutes = date.getMinutes();
	let seconds = date.getSeconds();
	hours = hours < 10 ? "0" + hours : hours;  
	minutes = minutes < 10 ? "0" + minutes : minutes;  
	seconds = seconds < 10 ? "0" + seconds : seconds;
	let str = year +'年'+ month+'月'+ day +'日'
	let str2 = hours + ":" + minutes + ":" + seconds
	let canvas = document.createElement('canvas');
	let context = canvas.getContext('2d');
	// 创建一个新的Image对象，用于加载原始图片
	let image = new Image();
	image.src = imagePath;
	// 在图片加载完成后执行下面的代码
	image.onload = function() {
		canvas.width = image.width;
		canvas.height = image.height;
		// 将原始图片绘制到canvas上
		context.drawImage(image, 0, 0);
		let size = image.width/20
		//将水印文本添加上
		context.font =  size+ "px Arial";
		context.fillStyle = "#FF0000"; // 设置填充颜色为红色  

		context.fillText(str + '  '+ str2, 20, size)
		if(mark){
				context.fillText(mark, 20, size*2)
		}
		// 将带有水印的图片转换为base64格式
		let watermarkedImage = canvas.toDataURL();
		calback&&calback(watermarkedImage)
	};
}

7. 效果