How to insert a new element at any position of a JS array?

Question

For getting a new array, you could concat the part an add a zero element for each element.

var array = ['a', 'b', 'c'],
    result = array.reduce((r, a) => r.concat(a, 0), [0]);
    
console.log(result);

Using the same array

var array = ['a', 'b', 'c'],
    i = 0;

while (i <= array.length) {
    array.splice(i, 0, 0);
    i += 2;
}

console.log(array);

A bit shorter with iterating from the end.

var array = ['a', 'b', 'c'],
    i = array.length;

do {
    array.splice(i, 0, 0);
} while (i--)

console.log(array);