sum.js

function range(start, end, step) {
    let arr = []
    if (step > 0){
        for (let index = start; index <= end; index += step) {
            arr.push(index)
        }
    } else if (step < 0)
    for (let index = start; index >= end; index += step) {
        arr.push(index)
    } else return "Err"
    return arr
}

function sum(array) {
    let sum = 0;
    array.forEach(item => {
        sum += item
    });
    return sum
}