learning how to do a unary function

simple_unary.js

const _ = {};

_.map = (arr, fn) => {
    const results = [];
    for(let i = 0; i < arr.length; i++) {
        results.push(fn(arr[i]));
    }
    return results;

};

_.unary = (fn) => {
    return (value) => {
        return fn(value);
    };
};

const result = _.map(['6', '8', '10'], _.unary(parseInt));