Search code examples
javascriptconstants

redeclare const variable in javascript

One of the key features of const in JavaScript is that the const variable cannot be redeclared.

However, in this code that is grabbed from this link:

signalServer.on('discover', (request) => {
  const clientID = request.socket.id // clients are uniquely identified by socket.id
  allIDs.add(clientID) // keep track of all connected peers
  request.discover(Array.from(allIDs)) // respond with id and list of other peers
})

Every time a new client connects to the server via a socket, a new const clientID = request.socket.id is created.

So the clientID variable is created more that one time even though it is a const.

How is that possible?

Solution

  • A variable name can only exist once in a scope. (Redeclaring one with var doesn't cause an error, doing so with let and const does).

    Each call to a function creates a new scope.

    There's still only one instance of that variable in that scope.