javascript - Nodejs array not working as expected -

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• why variable unaltered after modify inside of function? - asynchronous code reference 6 answers

i'm trying read in text file , store them in array of lease class. if console.log() inside final loop print loop in current state each iterration. if move console.log outside loop prints empty array.

working expected

const readline = require('readline'),   fs = require('fs');  function lease(renter, unit) {   this.unit = unit;   this.renter = renter; }  var list = [];  var rl = readline.createinterface({   input: fs.createreadstream('input.txt'),   output: process.stdout,   terminal: false });  rl.on('line', function(line) {   var values = line.split(' - ');   list.push(new lease(values[0], values[1]));   console.log(list); }); 

printing empty array

const readline = require('readline'),   fs = require('fs');  function lease(renter, unit) {   this.unit = unit;   this.renter = renter; }  var list = [];  var rl = readline.createinterface({   input: fs.createreadstream('input.txt'),   output: process.stdout,   terminal: false });  rl.on('line', function(line) {   var values = line.split(' - ');   list.push(new lease(values[0], values[1])); });  console.log(list); 

in first version, console.log() in callback function, executed when callback function invoked.

however, in second version, console.log() called before callback function of on.('line' executed...

the callback function async, won't executed until current stack empty...