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Update (write to) an object in a separate JS file using Node

I'm fairly new to Node, and am wracking my brains on how to achieve the following:
I have a config file that looks something like this:
// various es imports
export default {
input: {
index: 'src/index.ts',
Button: 'src/Button/index.ts',
Spinner: 'src/Spinner/index.ts',
'icons/Notification': 'src/_shared/components/icons/Notification.tsx',
'icons/Heart': 'src/_shared/components/icons/Heart.tsx',
},
//.. other properties
}
From my node script, i need to somehow read this file and do the following:
Delete any entries in the input object that have a key starting
with icons/
Append new entries to the input object.
Write these changes back to the original config file.
Is there a recommended way to do this in Node, i've been looking at a couple of libs, like replace-in-file but none seem to be suited to this particular case.

Just faced the same concern, here is how I solved it :
1. Gets your file content
If it is not a .js file, then use fs.readFileSync (or fs.readFile) like so :
const fs = require('fs');
const path = require('path');
const myObjectAsString = fs.readFileSync(
path.join( process.cwd(), 'my-file.txt' ), // use path.join for cross-platform
'utf-8' // Otherwise you'll get buffer instead of a plain string
);
// process myObjectAsString to get it as something you can manipulate
Here I am using process.cwd(), in case of a CLI app, it will gives you the current working directory path.
If it is a .js file (eg. a JavaScript config file like webpack.config.js for instance), then simply use require native function, as you would do with regular internal file or NPM module, and you will get all module.export content :
const path = require('path');
const myObject = require( path.join( process.cwd(), 'myFile.js') );
2. Modify your object as you want
// ...
myObject.options.foo = 'An awesome option value';
3. Then rewrite it back to the file
You can simply use fs.writeFileSync to achieve that :
// ...
fs.writeFileSync( path.join(process.cwd(), 'my-file.txt', myObject );
If you want to write a plain JavaScript Object, then you can use util.inspect() native method and you may also use fs.appendFileSync :
// ...
// If we wants to adds the 'module.exports = ' part before
fs.writeFileSync( process.cwd() + '/file.js', 'module.exports = ');
// Writes the plain object to the file
fs.appendFileSync( process.cwd() + '/file.js', util.inspect(options));

Simple node module command line example

I want to make a simple node module that can be run from the command line that I can input files into, then it might change every instance of 'red' to 'blue' for example and then save that as a new file. Is there a simple example out there somewhere that I can edit to fit my purposes? I've tried looking but couldn't find one that was sufficiently simple to understand how to modify it. Can anyone help?

A simple example of replace.js (both old and new files are supposed to be in UTF-8 encoding):
'use strict';
const fs = require('fs');
const oldFilePath = process.argv[2];
const newFilePath = process.argv[3];
const oldFileContent = fs.readFileSync(oldFilePath, 'utf8');
const newFileContent = oldFileContent.replace(/red/g, 'blue');
fs.writeFileSync(newFilePath, newFileContent);
How to call:
node replace.js test.txt new_test.txt
Documentation on used API:
process.argv
fs.readFileSync()
fs.writeFileSync()

NodeJs: fs.unlink does not delete file [VS]

I am aware this isn't the first post about fs.unlink not working, but I'm very new to both Visual Studio and Node Js.
I want to delete a file in the working folder, I got an error and the file is not deleted.
Here is what I tried:
var fs = require('fs');
fs.unlink('test1.txt');
PS: I installed the necessary Node Js components in VS.

As far as the code goes, you're not invoking fs.unlink properly. For starters, it's asynchronous. You will need to provide it a callback. See example here:
https://nodejs.org/api/fs.html#fs_fs_unlink_path_callback
Secondly, you need to provide it the full file path, not just the name of the file... ie:
var fs = require('fs');
fs.unlink('C:\path\to\my\file\test1.txt', (err) => {});
You can also supply it with the variable __dirname to utilize your current working directory from wherever you invoke node against the script. Thus, that would look something like:
let fs = require('fs');
let path = require('path');
fs.unlink(path.join(__dirname, 'test1.txt', (err) => {
if (err) throw err;
console.log('test1.txt was deleted');
});
Currently, you can also invoke it synchronously using it's single parameter signature... thus you'd provide only the dir path:
fs.unlinkSync('C:\\path\\to\\my\\file\\test1.txt');
But, this is ill-advised as it will be blocking. I'd only use the "sync" variant during some application bootstrapping process, where it'd be invoked only one time or so, at startup. Try to fight the urge of it being "easier" to use and understand, and instead get yourself to understand asynchronous logic.

Load text as JavaScript object in Node.js

I have a javascript file for node.js:
module.exports = {
someString: 'blblalb'
}
I want to able to read the file as a javascript object, using fs.readFileSync. I can't use require because I am using a variable that may be modified in runtime to load the file.
Is that possible?

You can use eval('JavaScript string') but is highly recommended not to. It is a serious security risk if you cannot 100% trust the source of the text. If a malicious user figures out a way to modify the text they have complete control of your system. It is not a path I would take or recommend.
const text = 'console.log("Hello")';
eval(text);
If I saw that code when I was doing a code review we would definitely be having some words.

it's possible to evaluate a file or string variable as child module in hacky yet valid way.
The problem is that Node.js module environment should be unaware of these operations. Child module may load other modules and contain require(...), it will fail if there is no require function (there is none if it is evaluated with vm) or it uses wrong module relative path (this will happen with eval), also there will be no dedicated module.exports for a module. This can be fixed by wrapping module source with Node.js module wrapper that was rewired to match child module location.
const fs = require('fs');
const Module = require('module');
const path = require('path');
const childModuleAbsPath = path.resolve('./foo/bar.js');
const childModuleBody = fs.readFileSync(childModuleAbsPath);
const childModuleObj = { exports: {} };
const { dir: childModuleDirname, base: childModuleFilename } = path.parse(childModuleAbsPath);
const childRequire = modulePath => module.require(childModuleAbsPath);
require('vm').runInThisContext(Module.wrap(childModuleBody))(
childModuleObj.exports,
childRequire,
childModuleObj,
childModuleDirname,
childModuleFilename
);
In this case childModuleObj.exports.someString === 'blblalb' after bar child module was evaluated.
This is XY problem that should be addressed in another way.
If the intention is to reevaluate a module with new variables, this can be done by invalidating Node module cache by modifying require.cache, e.g. with decache:
decache('./foo/bar');
const reloadedBar = require('./foo/bar');

Prototyping Built-In Modules in NodeJS

I've been trying to add some convenience functions to Node's file system module (mainly because it lacks some common sense things), but every time I begin fs.prototype.myfunc = in the repl, Node complains that I am trying to set a property of an undefined variable. Is it really true that you cannot access Node's built-in module prototypes from the outside? If so, does anyone know a feasible workaround to extend Node's built-in modules?
Just to note: I did require fs before trying to prototype it!
var fs = require('fs');
fs.prototype.myfunc = function() {}; //TypeError thrown here

What you get back in response to a require('') depends upon the particular module. Some modules do this:
module.exports = function() {}
in that case, the value returned would be function and so would have a prototype you could attach things to.
Other modules just set values on the already existing exports.module object. E.g:
module.exports.someFunc = function(){}
where module.exports is essentially just:
module.exports = {}
In the case of the fs module they do the latter:
var fs = exports;
....
fs.readFileSync = function(path, encoding) {
So you get the error you do since the object returned isn't a function. You'd get the same error if you did this:
var x = {};
x.prototype.myfunc = function(){}
Note you can just do:
var fs = require('fs');
fs.myFunc = function(){}

There might be a workaround, but node is sending you a message by not letting you monkey patch its modules. Doing require('fs-monkeypatch') to get extra functions in require('fs') is confusing. Just add your functions outside of the fs module.

Here's an example of how to do it:
https://github.com/mikeal/node-utils/blob/master/file/lib/main.js