How to download data created server-side with Node.js?

I want to retrieve some data from my REST API in Node to the user directly downloaded in json file when he clicks a link.

I tried some stuff using Blop, but it is not working in my case I don't understand why...

HTML

<div class='wrapper_align_vertical'>
        <a class='shortCut' id='extract'>Extract</a>
    </div>

JS (sample that is working)

Viewed this example on internet and worked well with sample data.

document.getElementById('extract').onclick = function(event){
    var data = { a: 1, b: "hello" }
    var json = JSON.stringify(data)
    var blob = new Blob([json], {type: "octet/stream"})
    var url = window.URL.createObjectURL(blob)

    this.href = url
    this.target = '_blank'

    // target filename
    this.download = 'data.json'
}

But in my case I am calling API to gather data from database before creating the blop.

How I am getting data

I am calling the API with ajax request.

function getFromDB(){
    return new Promise(function(resolve, reject){
        $.ajax({
            url: '/api/extract',
            dataType: "json",
            type: 'GET',
            headers: {
                "x-access-token" : getCookie('token')
            },
            success: function(data){
                resolve(data)
           }
        })
    })
}

What return the route /api/extract

The route get data from DB.

router.get('/', function(req, res, next){

    var query = 'SELECT ...'

    connection.query(query, function(err, rows){
        var result = []
        if(!err){
            for(label in rows){
                result.push(rows[label].path)
            }
            res.json({
                success: true,
                data:{
                    quantity : rows.length,
                    image: result
                }
            })
        }else{
            res.json({
                success: false,
                message: 'Failure while extracting tags from database !'
            })
        }
    })
})

What I want to do

But it is absolutely not working, maybe I am missing something ?

document.getElementById('extract').onclick = function(event){

    getFromDB()
    .then(function(data){
        var json = JSON.stringify(data)
        var blob = new Blob([json], {type: "octet/stream"})
        var url = window.URL.createObjectURL(blob)

        this.href = url
        this.target = '_blank'

        this.download = 'data.json'
    }, function(){
        // Promise failed
    })

}

If you have any advice or suggestion I'll appreciate, thank you !