Examples of iterating, mapping, filtering, and reducing arrays.

Node.js

const array = ["a", "b", "c"];

array.forEach((value, i) => {
  console.log(i, value);
});

const mapped = array.map((value) => {
  return value.toUpperCase();
});

console.log(mapped);

const filtered = array.filter((value, i) => {
  return i % 2 == 0;
});

console.log(filtered);

const reduced = array.reduce((acc, value, i) => {
  if (i % 2 == 0) {
    acc.push(value.toUpperCase());
  }

  return acc;
}, []);

console.log(reduced);

Output

0 'a'
1 'b'
2 'c'
[ 'A', 'B', 'C' ]
[ 'a', 'c' ]
[ 'A', 'C' ]

Go

package main

import (
	"fmt"
	"strings"
)

func main() {
	array := []string{"a", "b", "c"}

	for i, value := range array {
		fmt.Println(i, value)
	}

	mapped := make([]string, len(array))
	for i, value := range array {
		mapped[i] = strings.ToUpper(value)
	}

	fmt.Println(mapped)

	var filtered []string
	for i, value := range array {
		if i%2 == 0 {
			filtered = append(filtered, value)
		}
	}

	fmt.Println(filtered)

	var reduced []string
	for i, value := range array {
		if i%2 == 0 {
			reduced = append(reduced, strings.ToUpper(value))
		}
	}

	fmt.Println(reduced)
}

Output

0 a
1 b
2 c
[A B C]
[a c]
[A C]