javascript - Getting undefined node.js code -

i have code below. using readline , fs module trying search particular word in file line line , if word exist push contents of word array when try return array undefined. ideas?

var fs = require('fs'); var readline  = require('readline');  var reader = readline.createinterface({     input: fs.createreadstream('my_file_name.txt'), });  function newdefineword(reader1) {   this.reader = reader1; }    newdefineword.prototype.define = function(searchterm) {       var arr = [];        this.reader.on('line', function (line) {           if (line.search(searchterm)!== -1) {                         arr.push(line);             console.log(arr);           }       });        return arr;  }  var word = new newdefineword(reader); console.log(word.define('libro')); 

reader.on async returning before conclusion code should

    newdefineword.prototype.define = function(searchterm, cb) {           var arr = [];           this.reader.on('line', function (line) {                if (line.search(searchterm)!== -1) {                             arr.push(line);                 console.log(arr);               }         });         this.reader.on('close',function(){             cb(arr)         })      }      var word = new newdefineword(reader);     word.define('libro', function(arr){         console.log(arr);      }) 

additionally if not want use callbacks can use promises or generators