Various attempts to get an object to have an incrementing Id property

gistfile1.txt

[
{"id":1,"url":"http://www.ibm.com","cutUrl":"www.ibm.com"},
{"id":1,"url":"http://www.cnn.com","cutUrl":"www.cnn.com"},
{"id":1,"url":"https://www.cnn.com","cutUrl":"www.cnn.com"},
{"id":1,"url":"https://www.nintendo.com","cutUrl":"www.nintendo.com"}
]

//No matter what, the id is always 1 pretty much

postRequestCode.js

app.post('/api/shorturl/', body('url').isURL(), 
  
  (req, res) => {
    const errors = validationResult(req);
    if(errors.isEmpty()){
      //console.log(req.body)
      let url = req.body.url
      
      const url_without_protocol = url.replace(/^https?:\/\//, '')
      //above line source: https://stackoverflow.com/a/8206279/5456075
      console.log(url_without_protocol)
      dns.lookup(url_without_protocol, (err, address, family)=>{
        console.log(`address: ${address} family: IPv${family}`)
        
      })
      const shortenedLink = new ShortenedLink(req.body.url, url_without_protocol)
      shortenedLink.save()
      res.redirect(url)
    } else {
      res.send({error: 'invalid url'})
    }

})

ShortenedLinkScopingFunction.js

const fs = require('fs');
const path = require('path');

module.exports = Id =(() => {
    let lastId= 0;
    return class ShortenedLink {

    constructor(url, cutUrl){
        this.id = ++lastId
        this.url = url;
        this.cutUrl = cutUrl

    }

    static incrementId() {
        if(!this.latestId) this.latestId = 1
        else this.latestId++
        return this.latestId
    }

    save(){
        const p = path.join(
            path.dirname(require.main.filename),
            'data',
            'shortenedLinks.json'
        );
        fs.readFile(p, (err, fileContent) =>{
            let links = []
            if (!err) {
                links = JSON.parse(fileContent)
            }
            links.push(this)
            fs.writeFile(p, JSON.stringify(links), (err)=>{console.log(err)})
        })
    }
    static fetchAll(){
        const p = path.join(
            path.dirname(require.main.filename),
            'data',
            'shortenedLinks.json'
        );
        fs.readFile(p, (err,fileContent)=>{
            if (err){
                return [];
            }
            return JSON.parse(fileContent)
        })
        return links
    }
}})();

/*
last snippet at this link
*/

ShortenedLinkStaticMethod.js

const fs = require('fs');
const path = require('path');

module.exports = class ShortenedLink {

    constructor(url, cutUrl){
        this.id = ShortenedLink.incrementId()
        this.url = url;
        this.cutUrl = cutUrl

    }

    static incrementId() {
        if(!this.latestId) this.latestId = 1
        else this.latestId++
        return this.latestId
    }
  


    save(){
        const p = path.join(
            path.dirname(require.main.filename),
            'data',
            'shortenedLinks.json'
        );
        fs.readFile(p, (err, fileContent) =>{
            let links = []
            if (!err) {
                links = JSON.parse(fileContent)
            }
            links.push(this)
            fs.writeFile(p, JSON.stringify(links), (err)=>{console.log(err)})
        })
    }

    static fetchAll(){
        const p = path.join(
            path.dirname(require.main.filename),
            'data',
            'shortenedLinks.json'
        );
        fs.readFile(p, (err,fileContent)=>{
            if (err){
                return [];
            }
            return JSON.parse(fileContent)
        })
        return links
    }
}

  /*
  Based on code from this s/o response:
  https://stackoverflow.com/a/41916397/5456075
  
  */