前端面试宝典---前端水印

明水印

1. 背景图

通过css的background-image加载背景图

2. canvas+background水印

前端水印实现思路与示例代码

一、核心实现思路

Canvas动态生成水印
通过Canvas绘制文本或图案，将生成的图像转为Base64格式，作为背景图重复平铺到目标元素上。例如：

function createWatermark(text) {const canvas = document.createElement('canvas');const ctx = canvas.getContext('2d');canvas.width = 200;canvas.height = 150;ctx.font = '12px Arial';ctx.fillStyle = 'rgba(200,200,200,0.2)';ctx.rotate(-30 * Math.PI / 180); // 倾斜角度ctx.fillText(text, 10, 100);return canvas.toDataURL('image/png');
}

防篡改机制
- 使用MutationObserver监听DOM变化，若水印元素被删除则重新注入
- 禁止控制台操作：禁用右键菜单、屏蔽开发者工具快捷键
```
document.addEventListener('contextmenu', e => e.preventDefault());
```

容器绑定
将水印作为独立图层覆盖在目标内容上方，通过CSS确保全屏状态仍可见：

.watermark-container {position: relative;
}
.watermark-layer {position: absolute;pointer-events: none;z-index: 9999;background: url('data:image/png;base64,...');
}

二、完整示例代码

<!DOCTYPE html>
<html><body><style>.watermark-container {position: relative;}.watermark-layer {position: absolute;pointer-events: none;z-index: 9999;background: url('data:image/png;base64,...');}</style><div id="content">需要保护的内容</div><script>function createWatermark (text) {const canvas = document.createElement('canvas')const ctx = canvas.getContext('2d')canvas.width = 200canvas.height = 150ctx.font = '12px Arial'ctx.fillStyle = 'rgba(200,200,200,0.2)'ctx.rotate(-30 * Math.PI / 180) // 倾斜角度ctx.fillText(text, 10, 100)return canvas.toDataURL('image/png')}function initWatermark (text = '机密文件') {const watermark = document.createElement('div')watermark.style.backgroundImage = `url(${createWatermark(text)})`watermark.style.position = 'fixed'watermark.style.top = 0watermark.style.bottom = 0watermark.style.right = 0watermark.style.left = 0watermark.style.pointerEvents = 'none'// 防删除监听const observer = new MutationObserver(mutations => {if (!document.contains(watermark)) {document.body.appendChild(watermark)}})observer.observe(document.body, { childList: true })document.body.appendChild(watermark)}initWatermark('严禁复制');</script>
</body></html>

三、注意事项

动态水印
可添加时间戳、用户ID等可变信息增强追踪能力：
```
const dynamicText = `${username} ${new Date().toLocaleString()}`;
```
样式优化
- 使用background-repeat: repeat平铺
- 调整rgba透明度值平衡可见性与内容遮挡

跨框架实现
Vue/React可通过高阶组件封装水印逻辑，例如：

const withWatermark = (Component) => (props) => (<div className="watermark-wrapper"><Component {...props} /></div>
)

纯canvas水印

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Canvas水印示例</title><style>.watermark {position: fixed;top: 0;left: 0;right: 0;bottom: 0;z-index: 1000;pointer-events: none;opacity: 0.2;}</style>
</head>
<body><canvas id="watermarkCanvas" class="watermark"></canvas><div><h1>内容区域</h1><p>这是需要加水印的内容</p></div><script>window.onload = function() {var canvas = document.getElementById('watermarkCanvas');var ctx = canvas.getContext('2d');canvas.width = window.innerWidth;canvas.height = window.innerHeight;var text = '水印文本';var width = canvas.width;var height = canvas.height;ctx.font = '30px Arial';ctx.fillStyle = 'rgba(0, 0, 0, 0.1)';ctx.textAlign = 'center';ctx.textBaseline = 'middle';// 旋转并重复绘制水印文本for (var x = 0; x < width; x += 200) {for (var y = 0; y < height; y += 200) {ctx.save();ctx.translate(x, y);ctx.rotate(- Math.PI / 4);ctx.fillText(text, 0, 0);ctx.restore();}}};</script>
</body>
</html>

svg水印

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>SVG水印示例</title><style>.watermark {position: fixed;top: 0;left: 0;right: 0;bottom: 0;z-index: 1000;pointer-events: none;opacity: 0.2;}</style>
</head>
<body><div class="watermark"><svg width="100%" height="100%"><text x="50%" y="50%" dominant-baseline="middle" text-anchor="middle" font-size="30" fill="rgba(0,0,0,0.1)" transform="rotate(-45, 50, 50)">水印文本</text></svg></div><div><h1>内容区域</h1><p>这是需要加水印的内容</p></div>
</body>
</html>