Attempting to push object into array of objects turns it into an integer

Question

I need to create a new object and push it into an array of objects. When i try the code below it instead results in an integer which is the value of the array length.

const newThing = Object.assign(
            {},
            {
                __typename: 'Group',
                id: groupId,
            },
        );

        // userGroups is an array of strings eg ['1', '2']

        const newUserGroups = userGroups
            .map(item => {
                return Object.assign({}, { __typename: 'Group' }, { id: item });
            })
            .push( newThing );

        console.log(newUserGroups);

Answer 1

You could use Array#concat , because Array#push returns the new length of the array and concat returns a new array.

const newUserGroups = userGroups
        .map(item => {
            return Object.assign({}, { __typename: 'Group' }, { id: item });
        })
        .concat(newThing);

Answer 2

You are miss-implementing the chaining.

currently your chain is like this:

x = array.map().push()

so x will get the returned value of the last chained method ( push )

And push return the length of the array, not the array itself.

See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push

Remove the chain and it will be ok:

 const newThing = Object.assign({}, { __typename: 'Group', id: 'groupId', }, ); // userGroups is an array of strings eg ['1', '2'] const userGroups = ['1', '2']; const newUserGroups = userGroups .map(item => { return Object.assign({}, { __typename: 'Group' }, { id: item }); }); newUserGroups.push(newThing); console.log(newUserGroups);