使用方括号符号访问多个字符？

Question

I'm returning the 2nd, 3rd and 5th numbers in the string '123456' by using

function returnSome(numbers) {
  return numbers[1] + numbers[2] + numbers[4]
}

returnSome('123456'); //2, 3, 5

Simple enough right? What I'm wondering is whether there is a shorter way to write that out? something like numbers[1][2][4]?

I can't seem to find an answer online! (It may well be that I just don't know the correct terminology!)

Answer 1

Not really shorter, but you could use an array of indices and map that to the strings characters, then join them to a new string:

[1, 2, 4].map(i => numbers[i]).join("")

something like numbers[1][2][4]?

We can get quite close with currying:

const wrap = (str, res = "") => index => index + 1 ? wrap(str, res + str[index]) : res;

wrap(numbers)(1)(2)(4)()

Answer 2

You can turn the indices you want into a string that you iterate over and pull out from the array you pass in.

let returnSome = (numbers, sections) => sections.split("").map(i => +numbers[i]);

 let returnSome = (numbers, sections) => sections.split("").map(i => +numbers[i]); console.log( returnSome('123456', '124') ); //2, 3, 5