I have a file that has 6,000 of json. Its raw data and I need to add an comma ' , ' to the end of each line. Can someone help. Current code is creating a new line with a comma I need comma at end of each line. Node js or Javascript example is acceptable

The data file:

{"id": "67", "ac": []}
{"id": "78","ac": []}
{"id": "90", "ac": []}

What I am currently getting:

{"id": "67", "ac": []}
,
{"id": "78","ac": []}
,
{"id": "90", "ac": []}

What I need

{"id": "67", "ac": []},
{"id": "78","ac": []},
{"id": "90", "ac": []},

Current code

"use strict";

const fs = require("fs");

fs.readFile("users.json", (err, data) => {
  if (err) throw err;
  let student = data.toString();

  var lines = student.split(/(\n|\r\n)/);

  var new_content = lines
    .map(function (line) {
      return line + ",";
    })
    .join("\r\n");
  fs.writeFile("newFile.json", new_content, (err) => {
    if (err) throw err;
    console.log("Data written to file");
  });