Question

117

Using lodash, why is the map method within flow not working?

rated 0 times [ 119] [ 2] / answers: 1 / hits: 6163 / 6 Years ago, wed, september 12, 2018, 12:00:00

I have a users object am trying to use the lodash map() method on it to have it return only the userIds, while filtering out any users with the currentUserId. I wanted to avoid using chain() since it pulls in the entire library, so it seemed that the flow() method is perfect, yet it's not mapping to an array of Id's.

import {

  map, filter, flow,

} from 'lodash';



const users = {

    123: {

      uid: 123

    },

    456: {

      uid: 456

    }

};



const currentUserId = 123;



const userIds = flow(

  map(user => user.uid),

  filter(userId => userId !== currentUserId),

)(users);

Unfortunately, this is returning the same object as was passed into it. How can I get an array with the ids of all the users that are not the current user?

Answers

Only authorized users can answer the question. Please sign in first, or register a free account.

matteo

Add To Favorites

Follow

Total Points: 81

Total Questions: 100

Total Answers: 96

Location: Honduras

Member since Sat, Jul 24, 2021

3 Years ago

matteo questions

1 Differences between Lodash and Ramda

Tue, Mar 8, 22, 00:00, 2 Years ago

1 Javascript use single await in ternary operator

Sun, May 31, 20, 00:00, 4 Years ago

1 shuffle array in js

Thu, Mar 12, 20, 00:00, 4 Years ago

1 How to show placeholder when we hover on input type text

Tue, Jan 22, 19, 00:00, 5 Years ago

1 Creating multiple constructor in ES6

Sun, Jul 29, 18, 00:00, 6 Years ago

View All

answered 6 Years ago michelecarissab · Accepted Answer

The answer applies for the standard version of lodash. Please see @Vlaz's answer for a look at the functional programming version of lodash.

When you write _.map(user => user.uid) it is actually invoking the function at that time. What you're really attempting to do is to create function that is similar to _.map, but has one of its arguments already set.

Fortunately, Lodash has a built-in to handle this situation - _.partialRight

const userIds = _.flow(

  _.partialRight(_.map, user => user.uid)

  _.partialRight(_.filter, userId => userId !== currentUserId),

)(users);

Documentation

Alternatively if you wish to use plain JS rather than importing a new function, you can simply wrap it in an anonymous function to pass the arguments properly.

const userIds = _.flow(

  (users) => _.map(users, user => user.uid),

  (users) => _.filter(users, userId => userId !== currentUserId),

)(users);