Order of operations issue with + and ternary statements:

    console.log(0 + '' ? 'a' : 'b') // a

The code:

    freeLen + this.sockets[name] ? this.sockets[name].length : 0;

Is equivalent to:

    (freeLen + this.sockets[name]) ? this.sockets[name].length : 0;

When `this.sockets[name]` exists, it is an array, `(freeLen + this.sockets[name])` evaluates to a string, which evaluates to a string (true). When it does not, `(freeLen + this.sockets[name])` evaluates to `NaN` (false).
Either way, `freeLen` is ignored.