nodejs cookie-session typeerror - node.js

Question

TypeError: this.keys.index is not a function
the console log show that the if condition line is error
app.get('/',(req,res)=>{
if(!req.session.authenticated){
res.redirect('/login');
}else{
res.redirect('/search')
}
})
it was fine until i start another server.js from a completely different folder. I have tried to reinstall the node_module to fix it but it just result the same. but the weird part is i can start the server in a vm without any problem. can any help me with this?
Cookies.prototype.get = function(name, opts) {
var sigName = name + ".sig"
, header, match, value, remote, data, index
, signed = opts && opts.signed !== undefined ? opts.signed : !!this.keys
header = this.request.headers["cookie"]
if (!header) return
match = header.match(getPattern(name))
if (!match) return
value = match[1]
if (!opts || !signed) return value
remote = this.get(sigName)
if (!remote) return
data = name + "=" + value
if (!this.keys) throw new Error('.keys required for signed cookies');
index = this.keys.index(data, remote)
if (index < 0) {
this.set(sigName, null, {path: "/", signed: false })
} else {
index && this.set(sigName, this.keys.sign(data), { signed: false })
return value
}
};

Answer 1

I realise that this answer is late in the day but might help someone with the same error. I was getting the error 'TypeError: this.keys.index is not a function' on line 73 of index.js in cookies when trying to use koa-session.
I eventually realised that I had set app.keys to a single value i.e.
app.keys = 'dieueyf7huienejnfef'
When it should be an array:
app.keys = ['dieueyf7huienejnfef']