// Complete the following underscore functions.

// Reference http://underscorejs.org/ for examples.

const keys = (obj) => {

// Retrieve all the names of the object's properties.

// Return the keys as strings in an array.

// Based on http://underscorejs.org/#keys

return Object.keys(obj);

};

const values = (obj) => {

// Return all of the values of the object's own properties.

// Ignore functions

// http://underscorejs.org/#values

return Object.values(obj);

};

const mapObject = (obj, cb) => {

// Like map for arrays, but for objects. Transform the value of each property in turn.

// http://underscorejs.org/#mapObject

const keyArr = Object.keys(obj);

const result = {};

keyArr.forEach((k) => {

result[k] = cb(obj[k]);

});

return result;

};

const pairs = (obj) => {

// Convert an object into a list of [key, value] pairs.

// http://underscorejs.org/#pairs

return Object.entries(obj);

};

const invert = (obj) => {

// Returns a copy of the object where the keys have become the values and the values the keys.

// Assume that all of the object's values will be unique and string serializable.

// http://underscorejs.org/#invert

const keyArr = Object.keys(obj);

const result = {};

keyArr.forEach(k => result[obj[k]] = k);

return result;

};

const defaults = (obj, defaultProps) => {

// Fill in undefined properties that match properties on the `defaultProps` parameter object.

// Return `obj`.

// http://underscorejs.org/#defaults

const keyArr = Object.keys(defaultProps);

keyArr.forEach((k) => {

if (!obj[k]) {

obj[k] = defaultProps[k];

}

});

return obj;

};

/* eslint-enable no-unused-vars */

module.exports = {

keys,

values,

mapObject,

pairs,

invert,

defaults

};