// Complete the following underscore functions.

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

const keys = obj => Object.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

const values = obj => Object.values(obj);

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

// Ignore functions

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

const mapObject = (obj, cb) => {

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

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

for (let i = 0; i < keys(obj).length; i++) {

obj[keys(obj)[i]] = cb(values(obj)[i]);

}

return obj;

};

const pairs = (obj) => {

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

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

const outArr = [];

for (let i = 0; i < keys(obj).length; i++) {

const subArr = [];

subArr.push(keys(obj)[i], values(obj)[i]);

outArr[i] = subArr;

}

return outArr;

};

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 newObj = {};

for (let i = 0; i < keys(obj).length; i++) {

newObj[values(obj)[i]] = keys(obj)[i];

}

return newObj;

};

const defaults = (obj, defaultProps) => {

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

// Return `obj`.

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

for (let i = 0; i < keys(defaultProps).length; i++) {

if (obj[keys(defaultProps)[i]] === undefined) {

obj[keys(defaultProps)[i]] = values(defaultProps)[i];

}

}

return obj;

};

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

module.exports = {

keys,

values,

mapObject,

pairs,

invert,

defaults

};