Could not connect to websocket endpoint ws://localhost:4000/

[mrimran]

Unable to complete the subscriptions tutorial here https://www.howtographql.com/graphql-js/7-subscriptions/ due to this issue getting following error:

{
  "error": "Could not connect to websocket endpoint ws://localhost:4000/. Please check if the endpoint url is correct."
}

The schema that I'm sending in request is here:

subscription {
  newLink {
    node {
      id
      url
      description
      postedBy {
        id
        name
        email
      }
    }
  }
}

Here is the link to my repo: https://github.com/mrimran/hackernews

The above error is coming in Firefox whereas when I tried it on Chrome I'm facing the below issue which is already reported

#42

[mrimran]

I'm closing my issue as I was making a typo which I identified by closely looking at the code again.
The mistake was in the following code snippet inside Subscription.js
return context.db.subscription.link, the typo was subscribtion :)