I'm trying to retun number of my element that i research in a file but result of my return is undefined

function verifFile(file, element) {
var nb_element = 0;
var lectf = readline.createInterface({
    input: fs.createReadStream(file),
    console: false
});

lectf.on('line', function (line) {
    if (line.trim() != "") {        
        if (line.substring(N1, N2) == element) {
            nb_element++;
        }
    }
});
lectf.on('close', function () { 
    if (nombre_ligne_n == 0) {
        return nb_element;
    }
});

}test = verifFile(pathfile, element); ressult test is undefined