SOURCE

const log = console.warn

let reduce = function (reducer, initialValue) {
    let list = this
    let result = initialValue ?? list[0]
    let len = list.length
    for (let index = (initialValue !== undefined ? 0 : 1); index < len; index++) {
        result = reducer(result, list[index])
    }
    return result
}
Array.prototype.reduce = reduce
// log([1, 2].reduce((tol, cur) => tol + cur, ''))

let str = "aaabbc,2,cabc";
str = str.split('').reduce((tol, cur) => {
    if (tol[cur] === undefined) {
        tol[cur] = 1
    } else {
        tol[cur]++
    }
    return tol
}, {})
// log(str)

arr = [1, [2, 3, [4, 5, 6]], 7];
let flatten = function (arr) {
    return arr.reduce((tol, cur) => {
        if (Array.isArray(cur)) {
            return [...tol, ...flatten(cur)]
        } else {
            return [...tol, cur]
        }
    }, [])
}
// log(flatten(arr))

data = { b: { c: 4 }, d: [{ e: 5 }, { f: 6 }] }
let parse = function (obj, path) {
    let arr = path.split('.')
    return arr.reduce((tol, cur) => {
        return tol[cur]
    }, obj) || obj
}
// log(parse(data, 'd.1.f'))