How to add objects within another array of object at alternate position?

Question

I am working on a react component. Requirement is to add a new object at alternate position within array of object eg below:

arr1 = [{test: 1},{test: 2},{test: 3},{test: 4}]

expected output:

arr1 = [{test: 1},{dummy:1},{test: 2},{dummy:1},{test: 3},{dummy:1},{test: 4}]

is there a way to do the same in es6?

Answer 1

For getting your desired array, you could make of use the concat method in combination with reduce .

 var array = [{test: 1},{test: 2},{test: 3},{test: 4}]; var result = array.reduce((res, item) => res.concat(item, {dummy: 1}), []).slice(0, -1); console.log(result);

Since this adds {dummy: 1} object after each element from your array, just use

.slice(0, -1)

to add one exception for the last element from your given array.

If you want to modify the original array inplace , you could use splice method.

 var array = [{test: 1},{test: 2},{test: 3},{test: 4}]; for(i = 0;i < array.length - 1; i = i + 2){ array.splice(i + 1, 0, {dummy: 1}); } console.log(array);

Answer 2

I like to use map if I can. It is easier to understand and maintain.

So first create an array of array and then flatten it a single array with flat.

 let arr1 = [{test: 1},{test: 2},{test: 3},{test: 4}] arr1 = arr1.map(item=>[item,{dummy:1}]).flat().slice(0, -1) console.log(arr1);

Answer 3

To modify the original array (instead of creating an new one), you can first generate the indexes at which the new items need to be inserted, and then use Array.prototype.splice() :

 const a = [{test: 1}, {test: 2}, {test: 3}, {test: 4}]; Array.from({length: a.length - 1}, (_, i) => i * 2 + 1) .forEach(i => a.splice(i, 0, {dummy: 1})); console.log(a);