[Solved] edit JavaScript files using node js

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I was able to edit a JavaScript file using regex. my code is below:

  function updateFile(filename, replacements) {
            return new Promise(function(resolve) {
                fs.readFile(filename, 'utf-8', function(err, data) {
                    var regex, replaceStr;
                    if (err) {
                        throw (err);
                    } else {
                        regex = new RegExp("(\\" + 'let' + "\\s* ]*" + replacements[0].rule + "\\s*=\\s*)([^\\n;}]+)([\\s*;}])");
                            replaceStr = "$1" + replacements[0].replacer + "$3";
                            data = data.replace(regex, replaceStr);

                    }
                    fs.writeFile(filename, data, 'utf-8', function(err) {

                        if (err) {
                            throw (err);
                        } else {
                            resolve();
                        }
                    });
                });
            })
        }

usage:

var file = src/app.js
var myNewValue = "Hello";

     updateFile(file, [{
                rule: 'newApp',
                replacer: myNewValue
            }], function (err) {
                sails.log.info((err));
            });

this will edit, 

let newApp = lol; to let newApp = Hello;

solved edit JavaScript files using node js