Javascript Array count doesn't agree with console?

Question

Am I being stupid here? (I'm coming from Ruby, so there might be something about Javascript arrays that I'm missing).

console.log(new_devices)

Result in console: Array[1].

console.log(new_devices.length)

Result in console: 0

The code producing this:

var sp = require('serialport');
var new_devices = [];

sp.list(function(err, ports) {
  ports.forEach(function(current) {
    if (current.manufacturer == "Teensyduino") {
      new_devices.push(current);
    }
  });
});

console.log(new_devices);
console.log(new_devices.length);

You need to post the code that reproduces the issue. So far nobody can reproduce this. What does the `i` button next to the array say? Is something asynchronous going on? — Sebastian Simon, Sep 17 '16 at 14:37
Well I think it's pretty obvious that the desired behaviour is that the length printed to the console should agree with what Chrome thinks the length of the array is. Code added. — Alfo, Sep 17 '16 at 14:43
The code that populates `new_devices` sure looks asynchronous to me. — JohnnyHK, Sep 17 '16 at 14:45
Well that's confusing. Nothing about that looks asynchronous to me, but then I'm coming from Ruby and C... — Alfo, Sep 17 '16 at 14:47
@Alfo `sp.list` *is* asynchronous. Doesn't the docs state that? — Bergi, Sep 17 '16 at 14:48

score 2 · Answer 1 · answered Sep 17 '16 at 14:43

2

When you console log arrays the console creates a reference to that array, it does not show you a snapshot of the state of the array at the point of execution.

(In your code items are appended to the list async, so when the console log is printing the list is empty.)

Consider this example:

answered Sep 17 '16 at 14:43

knutesten

594
3
16

So how do I restructure this code in this so that I can get a correct number when I print `new_devices.length` to the console? – Alfo Sep 17 '16 at 14:53
Move you console.log to after you ports.forEach – knutesten Sep 17 '16 at 14:55

Javascript Array count doesn't agree with console?

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