How do I automatically get another users Steam ID?

[PlanZed]

Title says it all. I am currently trying to setup sending trading offers but I don't know how to get the Steam ID that it asks for.

[Dr. McKay]

How to get a user's SteamID depends on how you know what user you want to trade with.

[PlanZed]

1 hour ago, Dr. McKay said:

How to get a user's SteamID depends on how you know what user you want to trade with.

I am using Steam chat commands.  So when someone says "!buy x" it will send them a trade offer for the specific items on both parties.

[Dr. McKay]

The chatter's SteamID is available in the event that delivers you the chat message.

[PlanZed]

1 hour ago, Dr. McKay said:

The chatter's SteamID is available in the event that delivers you the chat message.

I know this is a dumb question but how would I call the SteamID from the chat message?

I have the code 

client.chatMessage(steamID, "Setting up the trade offer for Test Item");
const offer = manager.createOffer(steamID);

Is this the correct way to call it?

[Perport]

6 minutes ago, PlanZed said:

I know this is a dumb question but how would I call the SteamID from the chat message?

I have the code 

client.chatMessage(steamID, "Setting up the trade offer for Test Item");
const offer = manager.createOffer(steamID);

Is this the correct way to call it?

That should work but don't make the offer variable constant use var or let instead.