array data empty while sending it

Question


const express = require('express')
const fs = require('fs')
const router = new express.Router()
const readline = require('readline')

router.post('/api/tree-overview', async (req, res) => {
  try {
    var myInterface = readline.createInterface({
      input: fs.createReadStream('./ParsedTree.txt')
    })
    var array =  []
    myInterface.on('line', function(line) {
      array.push(line)
      console.log(line)
    })
    await res.send(array)
  } catch (e) {
    res.status(500).send(e)
  }
})

module.exports = router

res.send(array) is sending empty array how to make it wait for myInterface to finish running and send the data which is pushed.

There are several problems above, but the main conceptual problem is explained by the [linked question](https://stackoverflow.com/questions/23667086/why-is-my-variable-unaltered-after-i-modify-it-inside-of-a-function-asynchron)'s answers: Your `line` callbacks won't have run yet at the time you're doing `res.send(array)`; they're called **later**. (Other problems: 1. You never assign anything to `array` [you've fixed that now], so the first `array.push(line)` will throw an error because `array` is `undefined`. 2. `res.send` doesn't return a promise, so there's no reason to `await` it.) — T.J. Crowder, Feb 12 '20 at 15:04
To deal with the main problem, build up the array in response to `line` events as you are now, then do `res.send` in response to the [`close` event](https://nodejs.org/api/readline.html#readline_event_close) on the interface. Alternatively, use the fact that `Interface` is an async iterable by using `for-await-of` as shown [in one of the examples in the documentation](https://nodejs.org/api/readline.html#readline_example_read_file_stream_line_by_line)., then do `res.send` after the loop. — T.J. Crowder, Feb 12 '20 at 15:06

array data empty while sending it

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