edit JavaScript files using node js

Question

How can I find and edit an attribute value in a JavaScript file using nodeJS.

for example: If i have a file called app.js containing following code.

let title = "hello world";

document.getElementById("arr").innerHTML = title;

how can I change the value of title let title = "hello world"; or any other attribute using nodeJS.

Why do you want to programmatically change a JavaScript file? — Felix Kling
– Felix Kling, Commented Oct 25, 2017 at 6:18
While it is certainly possible,better approaches exist. For example use a config file, and import it in app.js, then edit/generate the config. Or, since you're going to use gulp anyway, substitute some variables in the compilation step. Also the question reads like a classic example of a XY Problem — pawel
– pawel, Commented Oct 25, 2017 at 6:27

Matt · Accepted Answer · 2017-10-25 07:37:10Z

0

Instead of trying to parse/edit JS files why not use something like JSON which is easy to serialize?

Your gulp task can write whatever values are needed to a file:

const fs = require('fs')
fs.writeFileSync('./blah.json', JSON.stringify({ title: "whatever" }))

Then your code references the JSON file

const title = require('./blah.json').title
document.getElementById("arr").innerHTML = title;

edited Oct 25, 2017 at 7:37

answered Oct 25, 2017 at 6:37

Matt

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3 Comments

Dilakshan Sooriyanathan Over a year ago

no the issue is my gulp file watches for changes on js files not only one file. there for I cannot use a seperate JSON file to store values, because from the above it only changes the json file values :/.

Matt Over a year ago

So modify the gulp watch? As @pawel mentioned, include detail explaining the actual process you are trying to achieve in the question. Editing javascript programatically is not likely to be the best solution to your problem.

Jonah Over a year ago

@DilakshanSooriyanathan stackoverflow.com/questions/30171340/… - this answer should explain how to get gulp to watch for changes to different files

Dilakshan Sooriyanathan · Accepted Answer · 2017-10-25 09:26:11Z

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;

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