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Exploring ES7's new Object methods

Monday, July 22nd, 2019

For a while now we have had the static Javascript method Object.keys(), a method that takes an object and returns the object's keys in an array, like so...

js

const dogs = {
Rocky: 'Bulldog',
Jeff: 'Poodle',
Sausage: 'Dachshund'
}
const dogKeys = Object.keys(dogs);

js

["Rocky", "Jeff", "Sausage"] //dogKeys

As you can see, we get back an Array containing 'Rocky', 'Jeff' and 'Sausage', the keys of our dog's object.

Object.keys() has been around for quite some time now so browser compatibility is great, but it is not without its flaws. Thankfully, ES7 brings two new Object methods to the specification to make our lives easier when working with Javascript Objects, these are Object.values() and Object.entries().

As you might have already guessed, Object.values() returns an array of the Object's values (basically the opposite to Object.keys()), whereas Object.entries() returns an array where each array item is an array containing a [key, value] pair for the object element.

Don't worry, this will make more sense when we look at some examples...

Using Object.values()

Here we have an object containing the ingredients for a delicious cake. To get the keys of the object, we can use our old friend Object.keys()...

js

const ingredients = {
eggs: 4,
lemons: 2,
sugar: '225g',
flour: '225g',
butter: '180g'
}
const ingredientKeys = Object.keys(ingredients);

js

["eggs", "lemons", "sugar", "flour", "butter"] // ingredientKeys

Now let's make use of Object.values() to get an array of all of the values within our ingredients object...

js

const ingredientValues = Object.values(ingredients);

js

[4, 2, "225g", "225g", "180g"] //ingredientValues

As you can see, Object.values() has given us an array containing all the values of our ingredients. Simple stuff so far, right? Now let's give Object.entries() a whirl...

Using Object.entries()

When you pass an object to Object.entries() it returns an array containing every [key value] pair of the object's properties.

Let's try it on our ingredients object...

js

const ingredientEntries = Object.entries(ingredients);

js

[
["eggs", 4],
["lemons", 2],
["sugar", "225g"],
["flour", "225g"],
["butter", "180g"]
]

Sweet! (No pun intended), we now have a neat array containing the [key value] pairs of all of our ingredients.

Where might Object.values() and Object.keys() be useful?

Let's imagine that our recipe object was given to us via a database request and we now want to display the ingredients to our users in an unordered list.

Previously, we may have used Object.keys() to achieve this by looping over each key and appending a new item to the list.

Here's is how that might look using Object.keys()...

js

const ul = document.querySelector('.ingredients');
Object.keys(ingredients).forEach(ingredient =>
ul.innerHTML += `<li>${ingredients[ingredient]} ${ingredient}</li>`
)

There is nothing wrong with this solution, but it could certainly be neater. When using Object.keys() we need to awkwardly fetch the item's value by accessing it via the ingredients object, which doesn't look too pretty.

Let's take a look at how Object.entries() could tidy this up. In this example we are not reaching outside of the loop to grab the ingredient object value, as Object.entries() gives us both the key and the value...

js

const ul = document.querySelector('.ingredients');
Object.entries(ingredients).forEach(([key, val]) => {
ul.innerHTML += `<li>${val} ${key}</li>`;
});

As Object.entries() returns an array for each object property, we can use ES6 destructuring to tidy things up. In this example we are immediately destructuring the key and value from the array and assigning them each to a variable that we can use in our function.

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You are reading the personal blog of Luke Brown, a freelance website designer and developer.