Array returned in function returns undefined

Question

Im trying to obtain an array with the path of the files contained in a directory. When returning the array, it returns "undefined". Here's the code:

var server = require('ws').Server;
var s = new server({ port : 8080 });
var fs = require('fs');

function searchImagePath(path){
    var array = [];
    fs.readdir(path, (err, files) => {
        array = files.map(file => path + "" + file);
    });
    return array;
}

s.on('connection', function(ws){
    ws.on('message', function(message){

        var pathImageList = searchImagePath("./img/");
        console.log("List: " + pathImageList);

    });

    ws.on('close', function(){
        console.log("I lost a client");
    });

});

It's a really simple question, but I've already spent 1 hour with this problem, and can't find a solution. Thanks