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Convert an array of objects to a Map in JavaScript

Here is the data we are going to be using in all the examples. It’s a simple array of objects that have the attributes name and completed. New Set() – creates the set, with optional iterable (e.g. array) of values for initialization. New Map() – creates the map, with optional iterable (e.g. array) of pairs for initialization. As we can see, unlike objects, keys are not converted to strings.

javascript convert array to map

On each iteration, use the Map.set() method to add the key value to the map. Call the forEach() method on the array to iterate through all objects. The Array.from() Unreal Engine Game Development static method creates a new, shallow-copied Array instance from an iterable or array-like object. You can omit index and array if you have no use for them.

You now have a few different ways to convert the values of a Map to an array in JavaScript. There may be some debate about which method is the most efficient but at the end of the day it all depends on your use case and what feels the most concise and readable to you. If you have any other creative methods or thoughts on the ones used here please leave us some feedback. The map.Keys() method gets the keys of the map and the map.entries() method is used to retrieve the map’s entries in a key-value pair.

Map.has – returns true if the key exists, false otherwise. Map.get – returns the value by the key, undefined if key doesn’t exist in map. Map is a collection of keyed data items, just like an Object. But the main difference is that Map allows keys of any type.

Convert Map Keys to an Array Using Spread Operator Method

The main feature is that repeated calls of set.add with the same value don’t do anything. That’s the reason why each value appears in a Set only once. Get access to our private community, all courses, and members only content for a low monthly price. Save posts, access exclusive content, join members-only communities and more. I’m a passionate and driven web developer with an eye for design and appreciation for the human aspect of technology.

We can also pass a Map directly to Array.from() as Map returns an iterable of pairs by default. We initialized the accumulator variable to a new Map object because that’s what we passed as the second argument to the reduce() method. Use the Array.reduce() method to iterate over the array.

  • In the below example, we will create an array of key/value pairs of object entries in todoList array using Object.entries() with Array.map().
  • The objects can also be accessed using Array.forEach(), however unlike Array.map() it always returns undefined instead of a new transformed array.
  • This is more readable than the top answer; however, it will iterate the array twice (once for the map call and once for the Object.fromEntries call).
  • The keys in Map are ordered while keys added to object are not.

The function we passed to theArray.reducemethod gets called for each element in the array. The function we passed to theArray.mapmethod gets called with each element in the array. We will consider an example of a to-do list which can be represented as an array of each item object with properties of the item name, price, quantity, isChecked, and brand details. The Javascript map() method in JavaScript creates an array by calling a specific function on each element present in the parent array. Generally, the map() method is used to iterate over an array and calling function on every element of the array. In this blog post, I will take you to examples of converting an array to a map with keys and values in javascript.

How to Convert JavaScript Map to Array of Objects?

In this example, we use reduce() method to convert an array of objects into a hash map containing key/value pairs created with property values. A list of all property values from the array of objects What should I learn before learning coding by Arnav Gupta Coding Blocks can be retrieved using Array.map() by returning the property value in the callback function. In the below example we create an array of all item_name values using Array.map() on todoList declaration.

javascript convert array to map

A Set is a special type collection – “set of values” , where each value may occur only once. We can use Object.fromEntries to get a plain object from Map. Using objects as keys is one of the most notable and important Map features. String as a key in Object is fine, but we can’t use another Object as a key in Object.

The keys of an Object are Strings and Symbols, whereas they can be any value for a Map, including functions, objects, and any primitive. Depending on your use case, if u need to need to have ordered keys, need to access the size of the map or have frequent addition and removal from the map, a Map is preferable. Also important to note that to get something out of a Map you need to use result.get as opposed to just result.

We have compiled all the necessary information related to converting map values to an array and also map keys and entries into an array using JavaScript. The Map constructor takes a two-dimensional array and returns a new Mapobject with all of the specified keys and values added to it. In this article, we’ll be looking at two ways to quickly convert an array of objects to a Map object in JavaScript.

Set is much better optimized internally for uniqueness checks. Set.delete – removes the value, returns true if value existed at the moment of the call, otherwise false. New Set() – creates the set, and if an iterable object is provided , copies values from it into the set. We’ve just seen how to create Map from a plain object with Object.entries. Map.delete – removes the element (the key/value pair) by the key. I started this blog as a place to share everything I have learned in the last decade.

Method 1: Convert Map Values to an Array Using Array.from() Method

To convert an array of objects to a map, you can use the Array.map() method to iterate through the array elements to create an array of key-value pairs. Then pass the array of key-value pairs to the Map() constructor to create a Map object. In order to add a new property to every object from the array of objects, the transformed object with a new property value has to be returned in the Array.map() callback function. We use the JavaScript spread operator to include all existing object property values along with the new properties that need to be added to object entries. Read more about spread operator from developer.mozilla.org/Operators/Spread_syntax.

javascript convert array to map

A Map may perform better in scenarios involving frequent addition and removal of key pairs. A Map is an iterable and can thus be directly iterated, whereas iterating over an Object requires obtaining its keys in some fashion and iterating over them. You can use Array.prototype.reduce() and actual JavaScript Map instead just a JavaScript Object.

Creating An Object from a Map

Isn’t using .map(…) pointless in this example as you don’t return anything in it? You can get the size of a Map easily with the size property, while the number of properties in an Object must be determined manually. Ayibatari Ibaba is a software developer with years of experience building websites and apps. He has written extensively on a wide range of programming topics and has created dozens of apps and open-source libraries.

Also note that any object can be used as the key and not just a string. @RyanShillington we are in an answer’s context here, which is Array.prototype.reduce as proposed by jmar777. Remember this is not a forum, you might want to read more about the SO Q/A structure.

I am experienced with building websites for small to medium businesses or large web applications for big businesses. Websites can be custom made using cutting edge technology and responsive design or created using the website builder of your choice. Use the keys() method on Map Object to get the keys of Map. JavaScript is How to Contribute to Open Source Projects A Beginner’s Guide best known for web page development but it is also used in a variety of non-browser environments. You can learn JavaScript from the ground up by following this JavaScript Tutorial and JavaScript Examples. First we will look at how to do this using the Array.reduce() method and then how to simplify things using for..of.