JavaScript实现手写签名，可触屏手写，支持移动端与PC端双端保存

// 获取DOM元素
var signatureArea = document.getElementById('signatureArea');
var clearButton = document.getElementById('clearButton');
var saveButton = document.getElementById('saveButton');

// 定义变量
var isDrawing = false; // 是否正在绘制
var lastX, lastY; // 上一个触摸点的坐标

3.创建两个canvas元素，并设置它们的宽度和高度

// 创建两个canvas元素
var drawingCanvas = document.createElement('canvas'); // 用于绘制签名
var backgroundCanvas = document.createElement('canvas'); // 用于保存带有白色背景的签名图像
var drawingCtx = drawingCanvas.getContext('2d'); // 获取绘制画布的上下文对象
var backgroundCtx = backgroundCanvas.getContext('2d'); // 获取背景画布的上下文对象
drawingCanvas.width = signatureArea.offsetWidth;
drawingCanvas.height = signatureArea.offsetHeight;
backgroundCanvas.width = drawingCanvas.width;
backgroundCanvas.height = drawingCanvas.height;

4.绑定触摸事件：touchstart, touchmove, touchend和click

// 绑定触摸事件
signatureArea.addEventListener('touchstart', startDrawing);
signatureArea.addEventListener('touchmove', draw);
signatureArea.addEventListener('touchend', stopDrawing);
clearButton.addEventListener('click', clearSignature);
saveButton.addEventListener('click', saveSignature);

5.实现触摸事件回调函数：startDrawing, draw和stopDrawing

// 开始绘制
function startDrawing(e) {
  e.preventDefault(); // 阻止默认事件
  var touch = e.touches[0]; // 获取触摸点坐标
  var rect = signatureArea.getBoundingClientRect(); // 获取签名区域的位置和大小
  lastX = touch.clientX - rect.left;
  lastY = touch.clientY - rect.top;
  isDrawing = true;
}

// 绘制中
function draw(e) {
  if (!isDrawing) return;
  var touch = e.touches[0];
  var rect = signatureArea.getBoundingClientRect();
  var x = touch.clientX - rect.left;
  var y = touch.clientY - rect.top;
  drawLine(lastX, lastY, x, y);
  lastX = x;
  lastY = y;
}

// 停止绘制
function stopDrawing() {
  isDrawing = false;
}

6.实现绘制线段的函数：drawLine

// 绘制实线
function drawLine(x1, y1, x2, y2) {
  drawingCtx.beginPath(); // 开始一条新的路径
  drawingCtx.moveTo(x1, y1); // 将画笔移动到起点
  drawingCtx.lineTo(x2, y2); // 绘制一条直线到终点
  drawingCtx.lineWidth = 1; // 设置线条的宽度为1像素
  drawingCtx.strokeStyle = '#000'; // 设置线条颜色为黑色
  drawingCtx.stroke(); // 绘制线条
}

7.实现清除签名的函数：clearSignature

// 清除签名
function clearSignature() {
  drawingCtx.clearRect(0, 0, drawingCanvas.width, drawingCanvas.height); // 清除绘制画布的内容
  backgroundCtx.clearRect(0, 0, backgroundCanvas.width, backgroundCanvas.height); // 清除背景画布的内容
}

8.实现保存签名的函数：saveSignature

// 保存签名
function saveSignature() {
  // 绘制白色背景
  backgroundCtx.fillStyle = 'white';
  backgroundCtx.fillRect(0, 0, backgroundCanvas.width, backgroundCanvas.height);

  // 复制绘制的签名到带有白色背景的画布
  backgroundCtx.drawImage(drawingCanvas, 0, 0);

  // 将带有白色背景的画布内容转为PNG格式的DataURL
  var dataURL = backgroundCanvas.toDataURL("image/png");

  // 创建一个链接元素并设置下载属性
  var link = document.createElement('a');
  link.href = dataURL;
  link.download = '签名.png'; // 设置下载文件的名称

  // 检查是否支持保存到相册
  if ("download" in link) {
    link.style.display = "none";
    document.body.appendChild(link);
    link.click();
    document.body.removeChild(link);
  } else {
    // 如果不支持保存到相册，你可以提供其他方式或提示用户手动保存
    alert("无法直接保存到相册，请手动保存签名图片。");
  }
}

9.将canvas元素插入DOM树中

// 将canvas元素插入DOM树中
signatureArea.appendChild(drawingCanvas);

10.完整代码



  
  
  
  
    body {
      font-family: Arial, sans-serif;
    }

    #signatureArea {
      width: 100%;
      height: 300px;
      border: 1px solid #ccc;
      margin-bottom: 20px;
    }

    button {
      padding: 10px 20px;
      font-size: 16px;
      background-color: #4CAF50;
      color: white;
      border: none;
      cursor: pointer;
      border-radius: 4px;
    }

    button:hover {
      background-color: #45a049;
    }
  


  
  
  

  
// 获取DOM元素
var signatureArea = document.getElementById('signatureArea');
var clearButton = document.getElementById('clearButton');
var saveButton = document.getElementById('saveButton');

// 定义变量
var isDrawing = false; // 是否正在绘制
var lastX, lastY; // 上一个触摸点的坐标

// 创建两个canvas元素
var drawingCanvas = document.createElement('canvas'); // 用于绘制签名
var backgroundCanvas = document.createElement('canvas'); // 用于保存带有白色背景的签名图像
var drawingCtx = drawingCanvas.getContext('2d');
var backgroundCtx = backgroundCanvas.getContext('2d');
drawingCanvas.width = signatureArea.offsetWidth;
drawingCanvas.height = signatureArea.offsetHeight;
backgroundCanvas.width = drawingCanvas.width;
backgroundCanvas.height = drawingCanvas.height;

// 绑定触摸事件
signatureArea.addEventListener('touchstart', startDrawing);
signatureArea.addEventListener('touchmove', draw);
signatureArea.addEventListener('touchend', stopDrawing);
clearButton.addEventListener('click', clearSignature);
saveButton.addEventListener('click', saveSignature);

// 开始绘制
function startDrawing(e) {
  e.preventDefault();
  var touch = e.touches[0];
  var rect = signatureArea.getBoundingClientRect();
  lastX = touch.clientX - rect.left;
  lastY = touch.clientY - rect.top;
  isDrawing = true;
}

// 绘制中
function draw(e) {
  if (!isDrawing) return;
  var touch = e.touches[0];
  var rect = signatureArea.getBoundingClientRect();
  var x = touch.clientX - rect.left;
  var y = touch.clientY - rect.top;
  drawLine(lastX, lastY, x, y);
  lastX = x;
  lastY = y;
}

// 停止绘制
function stopDrawing() {
  isDrawing = false;
}

// 绘制实线
function drawLine(x1, y1, x2, y2) {
  drawingCtx.beginPath();
  drawingCtx.moveTo(x1, y1);
  drawingCtx.lineTo(x2, y2);
  drawingCtx.lineWidth = 1;
  drawingCtx.strokeStyle = '#000';
  drawingCtx.stroke();
}

// 清除签名
function clearSignature() {
  drawingCtx.clearRect(0, 0, drawingCanvas.width, drawingCanvas.height);
  backgroundCtx.clearRect(0, 0, backgroundCanvas.width, backgroundCanvas.height);
}

// 保存签名
function saveSignature() {
  // 绘制白色背景
  backgroundCtx.fillStyle = 'white';
  backgroundCtx.fillRect(0, 0, backgroundCanvas.width, backgroundCanvas.height);

  // 复制绘制的签名到带有白色背景的画布
  backgroundCtx.drawImage(drawingCanvas, 0, 0);

  // 将带有白色背景的画布内容转为PNG格式的DataURL
  var dataURL = backgroundCanvas.toDataURL("image/png");

  // 创建一个链接元素并设置下载属性
  var link = document.createElement('a');
  link.href = dataURL;
  link.download = '签名.png'; // 设置下载文件的名称

  // 检查是否支持保存到相册
  if ("download" in link) {
    link.style.display = "none";
    document.body.appendChild(link);
    link.click();
    document.body.removeChild(link);
  } else {
    // 如果不支持保存到相册，你可以提供其他方式或提示用户手动保存
    alert("无法直接保存到相册，请手动保存签名图片。");
  }
}

// 将canvas元素插入DOM树中
signatureArea.appendChild(drawingCanvas);