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up vote 1 down vote favorite

How can I avoid the self variable here?

function urlBuilder(endpoint){
    var status = ["user_timeline", "home_timeline", "retweets_of_me", "show", "retweets", 
            "update", "update_with_media", "retweet", "unretweet", "retweeters", "lookup"
        ],
        friendships = ["incoming", "outgoing", "create", "destroy", "update", "show"]; 
    let endpoints = {
        status: status,
        friendships: friendships
    }

    var self = { };

    endpoints[endpoint].forEach(e => {
        self[e] = endpoint + "/" + e;
    });

    return self;

}

somewhat better, still an assignment statement. 

return [{}].map(el => {
  endpoints[endpoint].forEach(e => {
    el[e] = endpoint + "/" + e;
  });
  return el;
})[0];
share|improve this question

migrated from programmers.stackexchange.com Aug 24 at 6:26

This question came from our site for professional programmers interested in conceptual questions about software development.
    
Why would you want to? – Robert Harvey♦ Aug 24 at 3:52
1  
because it's midnight, mainly. just exploring. – Mega Man Aug 24 at 3:54
1  
In my understanding, your first approach was better. You are adding an extra and unnecessary iteration because of .map. Also, self is a conventional name for context variable. This will reduce the readability instead. – Rajesh Aug 24 at 7:46
    
@Rajesh I agree with the poor name, and agree that the second is less readable. – Mega Man Aug 24 at 12:45
up vote 4 down vote accepted

You cannot really. To create an object with a dynamic number of properties (and without using JSON.parse) you always need to mutate it by assignment or something similar.

Your best bet might be

return endpoints[endpoint].reduce((self, e) => {
    self[e] = endpoint + "/" + e;
    return self;
}, {});

which is quite functional.

share|improve this answer
up vote 1 down vote

You could use Object.assign too.

It does mutate the acc but it's localized to the reduce call.

endpoints[endpoint].reduce((acc, e) =>
  Object.assign(acc, { [e]: `endpoint/${e}` }), {})
share|improve this answer

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