SVG：可縮放矢量圖形（英語：Scalable Vector Graphics，SVG）是一種基於可擴展標記語言（XML），用於描述二維矢量圖形的圖形格式。 SVG由W3C制定，是一個開放標準。

(function () {
        // svg 實現 watermark
        function __svgWM({
                             container = document.body,
                             content = ‘請勿外傳‘,
                             width 
 
= ‘300px‘,
                             height = ‘200px‘,
                             opacity = ‘0.2‘,
                             fontSize = ‘20px‘,
                             zIndex = 1000
                         } = {}) {
            const args = arguments[0];
            const svgStr = `<svg xmlns="http://www.w3.org/2000/svg" width="${width}" height="${width}">
                          <text x="50%" y="50%" dy="12px"
                            text
 
-anchor="middle"
                            stroke="#000000"
                            stroke-width="1"
                            stroke-opacity="${opacity}"
                            fill="none"
                            transform="rotate(-45, 120 120)"
                            style="font-size: ${fontSize};">
                            ${content}
                          
 
</text>
                        </svg>`;
            const base64Url = `data:image/svg+xml;base64,${window.btoa(unescape(encodeURIComponent(svgStr)))}`;
            const __wm = document.querySelector(‘.__wm‘);

            const watermarkDiv = __wm || document.createElement("div");
            const styleStr = `
          position:absolute;
          top:0;
          left:0;
          width:100%;
          height:100%;
          z-index:${zIndex};
          pointer-events:none;
          background-repeat:repeat;
          background-image:url(‘${base64Url}‘)`;

            watermarkDiv.setAttribute(‘style‘, styleStr);
            watermarkDiv.classList.add(‘__wm‘);

            if (!__wm) {
                container.style.position = ‘relative‘;
                container.insertBefore(watermarkDiv, container.firstChild);
            }

            const MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
            if (MutationObserver) {
                let mo = new MutationObserver(function () {
                    const __wm = document.querySelector(‘.__wm‘);
                    // 只在__wm元素變動才重新調用 __canvasWM
                    if ((__wm && __wm.getAttribute(‘style‘) !== styleStr) || !__wm) {
                        // 避免一直觸發
                        mo.disconnect();
                        mo = null;
                        __svgWM(JSON.parse(JSON.stringify(args)));
                    }
                });

                mo.observe(container, {
                    attributes: true,
                    subtree: true,
                    childList: true
                })
            }

        }

        if (typeof module != ‘undefined‘ && module.exports) {  //CMD
            module.exports = __svgWM;
        } else if (typeof define == ‘function‘ && define.amd) { // AMD
            define(function () {
                return __svgWM;
            });
        } else {
            window.__svgWM = __svgWM;
        }
    })();

參考： http://web.jobbole.com/94960/

前端生成水印之SVG方式