用JS给H5页面增加水印

用JS给H5页面增加水印（watermark），代码示例如下：

import store from "../store";
export function waterMark() {
  (function waterMarkFulfill() {
    function textBecomeImg(text, fontsize, fontcolor) {
      var canvas = document.createElement("canvas");
      let buHeight = 0;
      if (fontsize <= 32) {
        buHeight = 99;
      } else if (fontsize > 32 && fontsize <= 60) {
        buHeight = 2;
      } else if (fontsize > 60 && fontsize <= 80) {
        buHeight = 4;
      } else if (fontsize > 80 && fontsize <= 100) {
        buHeight = 6;
      } else if (fontsize > 100) {
        buHeight = 10;
      }
      canvas.height = fontsize + buHeight;
      canvas.padding = 30;
      var context = canvas.getContext("2d");
      context.clearRect(0, 0, canvas.width * 2, canvas.height);
      context.textAlign = "center";
      canvas.width = 160;
      canvas.height = 130;
      context.fillStyle = fontcolor;
      context.font = fontsize + "px Arial";
      context.textBaseline = "middle";
      var lineHeight = 22;
      var lines = text.split("\n");
      context.fillText(lines[0], 40, fontsize / 2);
      context.fillText(lines[1], 28, fontsize / 2 + lineHeight);
      var dataUrl = canvas.toDataURL("image/png");
      return dataUrl;
    }
    var date = new Date();
    var time =
      date.getFullYear() +
      "-" +
      (date.getMonth() + 1).toString().padStart(2, "0") +
      "-" +
      date.getDate().toString().padStart(2, "0");
    var text = store.getters.realName + "\n" + time;
    var shuiyinDiv = document.createElement("div");
    var style = shuiyinDiv.style;
    style.position = "fixed";
    style.left = "-30%";
    style.top = "-60%";
    style.width = "200%";
    style.height = "200%";
    style.opacity = "0.1";
    style.background = "url(" + textBecomeImg(text, 16, "gray") + ")";
    style.zIndex = 9999999991;
    style.transform = "rotate(-30deg)";
    style.pointerEvents = "none";
    document.body.appendChild(shuiyinDiv);
  })();
}

效果如下：