Quick JS Question

QuickJSQuestion.js

var inventory = {
    '000001': {
        name: 'Banana Slicer',
        price: 2.99
    },
    '000002': {
        name: 'Three Wolves Tea Cozy',
        price: 14.95
    }        
};

function tenPercentOffOf (obj) {
    obj.price = Math.round(0.9 * obj.price * 100) / 100;
    return obj;
}

// INSTRUCTIONS
// 
// Please refer to the following Javascript variable declaration. When submitting your 
// application, please answer the following three questions at the top of your cover
// letter, before any salutations or headings.
//
// var bargainBananaSlicer = tenPercentOffOf(inventory['000001']);
//
// Question 1: After declaring that variable, what is the value of bargainBananaSlicer.price?
// Question 2: After declaring that variable, what is the price of the Banana Slicer 
//             in the inventory object?
// Question 3: Can you suggest ways to improve this code?



// Answer 1: bargainBananaSlicer.price would change to 2.69.
//
// Answer 2: Banana Slicer object in inventory would also change to 2.69.
//          Javascript is pass by value but not in array and objects.

// Answer 3: I suggest to create a shallow copy then update the copy and return it.
//          There are several ways to do it, see below functions.
//          Check sample benchmark for the following functions: http://jsben.ch/TsNfQ

// Using ES6 Object.assign
function tenPercentOffOf (obj) {
    return Object.assign({}, obj, { price:  Math.round(0.9 * obj.price * 100) / 100});
}

// Using lodash assign, I think it is based on ES6 Object.assign
function tenPercentOffOf (obj) {
    return _.assign({}, obj, { price: Math.round(0.9 * obj.price * 100) / 100});
}

// Using lodash copy
function tenPercentOffOf (obj) {
    let copy =  _.clone(obj);
    copy.price = Math.round(0.9 * copy.price * 100) / 100;
    return copy;
}

// Using JSON parse and stringify
function tenPercentOffOf (obj) {
    var copy = JSON.parse(JSON.stringify(obj));
    copy.price = Math.round(0.9 * obj.price * 100) / 100;
    return copy;
}