How to return a value from nested javascript function?

Question

window.RTCPeerConnection = window.RTCPeerConnection || window.mozRTCPeerConnection || window.webkitRTCPeerConnection;  
var pc = new RTCPeerConnection({iceServers:[]}), noop = function(){};      
pc.createDataChannel("");   
pc.createOffer(pc.setLocalDescription.bind(pc), noop);        
pc.onicecandidate = function(ice){ 
  if(!ice || !ice.candidate || !ice.candidate.candidate)  return;
  ice.candidate.candidate.split('\r\n').forEach(function (line) {   
    if (line.indexOf("candidate")!==-1) {           
      var parts = line.split(' '),             
      addr = parts[4],
      type = parts[7];
      if (type === 'host') {
        console.log(addr);
        return addr;
      }
    } 
  });
  pc.onicecandidate = noop;
};

In the above javascript, the console.log(addr) works but not the return. Please point me where I am doing wrong. I tried to wrap this in a function and that doesn't work it either.

return addr; will return from the .forEach callback but that doesn't do anything at all - the .forEach just continues with the next thing. Use a normal loop or perhaps .find() - note that .find() doesn't transform the value, it just returns the item from the array where the callback returned a truthy value. — VLAZ
– VLAZ, Commented Apr 27, 2021 at 19:56
This might help with how to think about callbacks/"nested" functions: felix-kling.de/blog/2019/… — Felix Kling
– Felix Kling, Commented Apr 27, 2021 at 20:12
You could just use for (const line of ice.candidate.candidate.split('\r\n')) { ... } instead of forEach to make your code work. — Felix Kling
– Felix Kling, Commented Apr 27, 2021 at 20:14

Matt Styles · Accepted Answer · 2021-04-27 20:21:46Z

1

pc.onicecandidate = function(ice){ 
  if(!ice || !ice.candidate || !ice.candidate.candidate)  return;

  const hosts = [];

  ice.candidate.candidate.split('\r\n').forEach(function (line) {   
    if (line.indexOf("candidate")!==-1) {           
      var parts = line.split(' '),             
      addr = parts[4],
      type = parts[7];
      if (type === 'host') {
        console.log(addr);

        hosts.push(addr)

      }
    }
  });
  pc.onicecandidate = noop;
  
  return hosts;
};

Is something like that what you are after?

You want to return each host address?

This stores the hosts locally. Foreach is synchronous so when it has completed working on the collection then your function will reach the return statement.

If you want to find the first address then you might want to use .find instead of .forEach, or check that a value exists and bail from the forEach when it does (note that you're still calling that function on each item, it'll just return straight away). You can break out of a forEach but its not idiomatic, you'd have to throw an exception and you try..catch, a bit nasty in JS and not really the intended use for the syntax.

pc.onicecandidate = function(ice){ 
  if(!ice || !ice.candidate || !ice.candidate.candidate)  return;

  const line = ice.candidate.candidate.split('\r\n').find(function (line) {   
    if (line.indexOf("candidate")!==-1) {           
      var parts = line.split(' ');
      var type = parts[7];
      return type === 'host'
    }
  });
  pc.onicecandidate = noop;
  return line.split(' ')[4]
};

Something like this I think should work for .find. .find will return the item, which you can then pull the addr from. Alternatively you could let addr outside, update that inside, then ignore the return value from .find. Oh, you'll want to add something if your .find returns nothing, or things will break when you try to split it and pull something out.

edited Apr 27, 2021 at 20:21

answered Apr 27, 2021 at 20:07

Matt Styles

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3 Comments

Learner Over a year ago

Exactly this is what I am looking after. I just want to return just only one value which is the first address. Any example of using .find to return the first address, please?

Matt Styles Over a year ago

Added to the answer. I think that should work for a .find.

Matt Styles Over a year ago

No problem. Using WebRTC sounds like a really interesting project. Best of luck to you!

Slava Knyazev · Accepted Answer · 2021-04-27 20:03:21Z

1

As long as your code in synchronous, you can write variables outside of the immediate function scope like so:

let result = null;
ice.candidate.candidate.split('\r\n').forEach(function (line) {   
    if (line.indexOf("candidate")!==-1) {           
      var parts = line.split(' '),             
      addr = parts[4],
      type = parts[7];
      if (type === 'host') {
        console.log(addr);
        // Save value
        result = addr;
      }
    } 
  });
// ...
console.log(result);

This can be further improved by using a for (let .. of ..) loop and break to stop the loop after finding the value you're looking for.

You should also consider Array.prototype.find() for this.

answered Apr 27, 2021 at 20:03

Slava Knyazev

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2 Comments

Learner Over a year ago

instead of console.log(result); shall i get return(result) in another function?

Slava Knyazev Over a year ago

You can return result in any scope below the declaration. Is that what you mean?

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