How to implement an online electronic signature system using WebSocket and JavaScript

How to use WebSocket and JavaScript to implement an online electronic signature system

Overview:
With the advent of the digital age, electronic signatures are widely used in various industries. to replace traditional paper signatures. As a full-duplex communication protocol, WebSocket can perform real-time two-way data transmission with the server. Combined with JavaScript, an online electronic signature system can be implemented. This article will introduce how to use WebSocket and JavaScript to develop a simple online electronic signature system, and provide some specific code examples.

1. Preparation

1. Create an HTML page: Create an HTML page to display the signature interface.
2. Introduce the WebSocket library: Introduce the WebSocket library, such as Socket.io, into the HTML page.
3. Introduce JavaScript files: Create a JavaScript file to implement signature logic.

2. Develop signature function

1. Generate canvas: Use the Canvas element of HTML5 to create a canvas for users to sign on it.

   <canvas id="signatureCanvas" width="600" height="300"></canvas>

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2. Get the signature data on the canvas: Use JavaScript code to get the user's signature data on the canvas.

   var canvas = document.getElementById("signatureCanvas");
   var context = canvas.getContext("2d");
   var isDrawing = false;
   var lastX = 0;
   var lastY = 0;
   
   canvas.addEventListener("mousedown", function(e) {
     isDrawing = true;
     [lastX, lastY] = [e.offsetX, e.offsetY];
   });
   
   canvas.addEventListener("mousemove", function(e) {
     if (!isDrawing) return;
     context.beginPath();
     context.moveTo(lastX, lastY);
     context.lineTo(e.offsetX, e.offsetY);
     context.stroke();
     [lastX, lastY] = [e.offsetX, e.offsetY];
   });
   
   canvas.addEventListener("mouseup", function() {
     isDrawing = false;
   });
   
   function getSignatureData() {
     return canvas.toDataURL();
   }

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3. Send signature data to the server: Use WebSocket to send the user's signature data to the server.

   var socket = io(); // 初始化WebSocket
   
   function sendSignatureData(signatureData) {
     socket.emit("signatureData", signatureData);
   }

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3. Server-side processing of signature data

1. Receive signature data: Use the WebSocket server to receive signature data from the client.

   var io = require("socket.io")(server);
   
   io.on("connection", function(socket) {
     socket.on("signatureData", function(signatureData) {
    // 处理签名数据
     });
   });

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2. Processing signature data: Process the received signature data on the server side, and save the signature data to a database or file system according to actual needs.

   socket.on("signatureData", function(signatureData) {
     // 处理签名数据
     saveSignatureData(signatureData);
   });
   function saveSignatureData(signatureData) {
     // 将签名数据保存到数据库或文件系统中
   }

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4. Display the signature result

1. The client receives the signature result: Use the WebSocket client to receive the signature result returned by the server.

   socket.on("signatureResult", function(result) {
     // 处理签名结果
     displaySignatureResult(result);
   });

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2. Display signature results: Display the signature results in the HTML page.

   function displaySignatureResult(result) {
     var resultElement = document.getElementById("signatureResult");
     resultElement.innerHTML = result;
   }

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3. The server sends the signature result: After processing the signature data, the server sends the signature result to the client.

   function sendSignatureResult(result) {
     socket.emit("signatureResult", result);
   }

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Summary:
This article introduces how to use WebSocket and JavaScript to develop a simple online electronic signature system. Through the two-way communication capability of WebSocket, real-time data transmission and processing can be achieved, making the user's signature operation simpler and more efficient. Through the implementation of the above steps, we can easily build an online electronic signature system and expand and optimize it according to actual needs.

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