Fix hardcoded path for error.log and move errorLog() to UptimeKumaServer.errorLog()

server/uptime-kuma-server.js

@@ -5,13 +5,14 @@ const http = require("http");
 const { Server } = require("socket.io");
 const { R } = require("redbean-node");
 const { log } = require("../src/util");
+const Database = require("./database");
+const util = require("util");
 
 /**
  * `module.exports` (alias: `server`) should be inside this class, in order to avoid circular dependency issue.
  * @type {UptimeKumaServer}
  */
 class UptimeKumaServer {
-
     /**
      *
      * @type {UptimeKumaServer}
@@ -83,6 +84,32 @@ class UptimeKumaServer {
 
         return result;
     }
+
+    /**
+     * Write error to log file
+     * @param {any} error The error to write
+     * @param {boolean} outputToConsole Should the error also be output to console?
+     */
+    static errorLog(error, outputToConsole = true) {
+        const errorLogStream = fs.createWriteStream(Database.dataDir + "/error.log", {
+            flags: "a"
+        });
+
+        errorLogStream.on("error", () => {
+            log.info("", "Cannot write to error.log");
+        });
+
+        if (errorLogStream) {
+            const dateTime = R.isoDateTime();
+            errorLogStream.write(`[${dateTime}] ` + util.format(error) + "\n");
+
+            if (outputToConsole) {
+                console.error(error);
+            }
+        }
+
+        errorLogStream.end();
+    }
 }
 
 module.exports = {