In contrast, the functional paradigm using map has more of a 'pipeline' approach, where the flattening, sorting, and filtering operations are more clearly discerned as separate steps.
![nodejs map nodejs map](http://3.bp.blogspot.com/-pbGjACYiUF4/UPW_I4nYioI/AAAAAAAAAtM/3ZYoWqCb-r0/s1600/Google_Maps_JavaScript_API_v3_Example__Geocoding_Simple.png)
keys (indexedPeople ) for ( let i = 0 i = 21 ) sort (peopleArray )Īn important thing to note is that the imperative example mixes the flattening and filtering operations in the same 'stage' of the computation. The simplest application of reduce I can think of is summing up an array of numbers:Ĭonst peopleArray = const keys = Object. I am hoping these benefits will become evident as I explore the map and reduce patterns below. Encourages cleaner separation of concerns.Elimination of the use of mutable data structures and variables which leave room for unintended side effects.However there are some advantages to using Map / Reduce over these imperative techniques: Its possible to achieve the transformations I mentioned above with traditional imperative techniques, largely involving for loops and mutable data structures.
![nodejs map nodejs map](https://nodejs.org/static/images/logo-hexagon-card.png)
A large portion of the rest of this blogpost are examples of variations on these two themes. Likewise, I use the reduce function if I find it necessary to take an array of objects and boil it down to a non-array structure (either a primitive or some JSON object). Generally speaking, I turn to the map function if I need to transform some Array of one object type into another Array of a different object type. I'd like to share some of the common map and reduce patterns I've come to use frequently in this blogpost, contrasting these techniques with the corresponding traditional imperative approach.
NODEJS MAP CODE
sort etc) and ES6 have made my code more expressive and easier to understand. These functions (in conjunction with other classic favorites such as. In particular I've discovered the joy of using Map and Reduce. Map.forEach((value) => result.push(value)) Ĭonsole.log(getValuesFirstApproach(users)) Ĭonsole.log(getValuesSecondApproach(users)) Ĭonsole.Over the past couple of months I've started to become a little bit more serious in applying functional programming techniques to my favorite client side language, JavaScript. If you have any other creative methods or thoughts on the ones used here please leave us some feedback. 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. While the Map object is not the most popular, it definitely has a place in your toolkit when it comes to creating a list of data - especially if the order matters and you want to be able to access each piece of data quickly and easily. You now have a few different ways to convert the values of a Map to an array in JavaScript. This solution is similar to the previous one but simply spreads the values into an array rather than using the om() method. The final solution feels the most modern since it uses the ES6 spread syntax:
![nodejs map nodejs map](https://cdn-images-1.medium.com/max/1600/1*3WBdCY6R2sTuM0QQAt93Aw.png)
This is a shallow-copied array so keep that in mind if you are using this with any objects with deeply-nested properties. Luckily, the om() method takes such an iterator object and creates a new array. Since this is just the iterator for the values, you will still need to iterate those values before you get your result. This method returns an iterator object for the values contained by the Map. But can it be improved?Ĭonst result = om(users.values())
![nodejs map nodejs map](https://www.tutorialspoint.com/nodejs/images/nodejs_concepts.jpg)
This is an easy solution and realistically there is nothing wrong with it. When iterating a JavaScript Map, each entry represents the value of that key-value pair. In this solution, we create an array result to store the values and iterate through the Map, adding each value to the array. Users.forEach((user) => result.push(user)) In these examples we’ll use the simpler Map from above where the values are just strings for brevity. The first way may come to mind if you have not used Maps many times before. JavaScript Map objects are iterable so that leaves us a few different ways to approach accessing a Map’s values. Now that we have a Map and a general understanding of its purpose, how would we go about actually retrieving the values of the Map? Specifically, how do we convert the values of the Map to an array? The solution For example, let’s say you have the same users except you’d like to store more information than just their username: The fun part about using Maps is that the key-value pairs can be even more than just primitive values. Maps can be particularly useful for storing simple key-value pairs such as IDs and usernames: Introduced as part of the ECMAScript 2015 (ES6) specification (and not to be confused with the () method), the Map object stores an ordered list of key-value pairs. JavaScript has many lesser known yet useful features.