Getting undefined node.js code

Question

I have this code below. Using the readline and fs module I am trying to search for a particular word in a file line by line and if that word exist push the contents of that word to an array but when I try to return this array I get an undefined. Any 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'));

I'm not a node expert but the way JS works which seems like the return arr is being retuened before the function gets executed, it's async, right? Check this. — The Alpha
– The Alpha, Commented Feb 7, 2016 at 23:33

FabioCosta · Accepted Answer · 2016-02-07 23:36:34Z

1

reader.on is async you are returning it before the conclusion your code should be

    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 you do not want to use callbacks you can use promises or generators

answered Feb 7, 2016 at 23:36

FabioCosta

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1 Comment

Tj1234 Over a year ago

Thanks will take a look at promises and emitters also, currently learning a lot at the moment just from this small exercise

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