How to insert a new element in between all elements of a JS array?

Question

I have an array [a, b, c]. I want to be able to insert a value between each elements of this array like that: [0, a, 0, b, 0, c, 0].

I gues

Answer 1

Another way:

var a = ['a', 'b', 'c'],
  b;

b = a.reduce((arr, b) => [...arr, b, 0], []);

console.log(b);

Answer 2

let arr = ['a', 'b', 'c'];

function insert(items, separator) {
  const result = items.reduce(
    (res, el) => [...res, el, separator], [separator]);
  return result;
}

console.log(insert(arr, '0'));

Answer 3

Another ES6+ version using flatmap (if creation of a new array instead is ok):

['a', 'b', 'c', 'd']
    .flatMap((e, index) => index ? [e, 0] : [0, e, 0])

Answer 4

Another way if you want to exclude the start and end of array is :

var arr = ['a', 'b', 'c']
var newArr = [...arr].map((e, i) => i < arr.length - 1 ? [e, 0] : [e]).reduce((a, b) => a.concat(b))

console.log(newArr)

Answer 5

You can use map() with ES6 spread syntax and concat()

var arr = ['a', 'b', 'c']
var newArr = [0].concat(...arr.map(e => [e, 0]))

console.log(newArr)

Answer 6

You can try with the below code. It will add 0 in middle of each two element of the array

console.log(['a', 'b', 'c'].reduce((r, a) => r.concat(a,0), [0]).slice(1, -1))