- But the main difference is that Map allows keys of any type.
- Map.delete – removes the element by the key, returns true if key existed at the moment of the call, otherwise false.
- We can also pass a Map directly to Array.from() as Map returns an iterable of pairs by default.
- I started this blog as a place to share everything I have learned in the last decade.
Map.delete – removes the element by the key, returns true if key existed at the moment of the call, otherwise false. A call to map.entries() returns an iterable of key/value pairs, exactly in the right format for Object.fromEntries. We will consider an example 113 Best Places to Learn to Code For Free Coding for Beginners 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. Finally, we pass the result to the Map() constructor to create a new instance of the Map object.
Iteration over 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. Iterate over every object and perform “delete object.property_name” to permanently delete the property from the reference object. I am an academic researcher and love to learn and write about new technologies.
Further, we used nested Array.map() to convert brand_details object into key/value pair array. Another way to transform the map’s values into an array is to use the “spread operator” with the “map.values()” method. The map.values() method first gets the map’s values, and the spread operator will copy all the map values into an array. In the below example, the “brand_details” property is deleted from todoList array by excluding it in the return object of the callback function inside Array.map().
That’s for compatibility with Map where the callback passed forEach has three arguments. But this may help to replace Map with Set in certain cases with ease, and vice versa. Set.has – returns true if the value exists in the set, otherwise false. 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.
The map.values() method is used to get the values of the map and the Array.from() method converts these values to an array. If provided, every value to be added to the array is first passed through this function, and mapFn’s return value is added to the array instead. We passed a two-dimensional array containing key-value pairs directly to theMap()constructor. The function we passed to theArray.reducemethod gets called for each element in the array.
When the this value is not a constructor, a plain Array object is returned. If the arrayLike object is missing some index properties, they become undefined in the new array. ArrayLike An iterable or array-like object to convert to an array.
Creating List from Array of Objects
Then use the array.from() method to convert a map object to an array. An array of objects are a list of object enclosed in , each object holds key and value pairs. For converting the values of a map to an array, use the “map.values()” method with the “Array.from()” method.
To create a Map from Object, we can convert an object into an array of pairs and then create a Map using it. Use the Map() constructor to convert a two-dimensional array to a Mapobject. Pass the array of the key-value pairs to the Map() constructor.
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.
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. 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.