split string in two on given index and return both parts

I have a string that I need to split on a given index and then return both parts, seperated by a comma. For example:

string: 8211 = 8,211
        98700 = 98,700

So I need to be able to split the string on any given index and then return both halves of the string. Built in methods seem to perform the split but only return one part of the split.

string.slice only return extracted part of the string. string.split only allows you to split on character not index string.substring does what I need but only returns the substring string.substr very similar - still only returns the substring

Solution 1:

Try this

function split_at_index(value, index)
{
 return value.substring(0, index) + "," + value.substring(index);
}

console.log(split_at_index('3123124', 2));

Solution 2:

ES6 1-liner

// :: splitAt = number => Array<any>|string => Array<Array<any>|string>
const splitAt = index => x => [x.slice(0, index), x.slice(index)]

console.log(
  splitAt(1)('foo'), // ["f", "oo"]
  splitAt(2)([1, 2, 3, 4]) // [[1, 2], [3, 4]]
)