编辑代码

function sum(arr) {
    return arr.reduce((pre, cur) => pre + cur, 0)
}

function sum(arr) {
    let rest

    if (arr.length > 0) {
        rest = arr.slice(1)
    } else {
        return 0
    }

    return arr[0] + sum(rest)
}

console.log(sum([2, 4, 6]))
console.log(sum([4, 6]))
console.log(sum([0, 6]))
console.log(sum([-1, 6]))