filter() follows the same syntax as map(). filter() is written similarly to map() and it also creates a new array, but its function performs a test and filters out everything that doesn't pass. At first, I thought about using filter() to find out how many instances of each neighborhood name were found throughout the feed. We have all the data we need in the JSON file, but I wasn't sure how to succinctly count all the instances. With such a small example, of course it would be very easy to simply write "Rogers Park: 1 Wicker Park: 2", but the longer it gets and the more neighborhoods and cafes get added, the more of a need there will be to automate this process. In our example, we have two neighborhoods for the three cafes - one in Rogers Park, and two in Wicker Park. I wanted to make a count of how many cafes I visited in each neighborhood. Each cafe was in a neighborhood, and I had a few neighborhoods that had more than one cafe that I had visited. There were three cafes in our reduced example, but I ended up with around a dozen. Using filter() to find matching valuesĪt this point, I had a map with all my markers created. home html5 css3 javascript jquery bootstrap5 v4. This use case of map() technically works, but since cafes will contain an empty array, forEach() would also be a good choice for this situation. Of course, map() is capable of much more than what we're doing in this example, but it's a good and practical start. It can be a bit tricky to keep track of all the square and curly brackets at first. If you've never used JSON before, I would strongly suggest reading this JSON tutorial to learn all about it from scratch and do some practice.Īt this point, I will delete all the marker information from scripts.js and make a JSON file with an object containing an array containing objects of all my coffee house locations. It would be much easier to create a JSON file, and loop through that. It executes the given reducer function for each element of the array except empty values, resulting in a single output value. Now it can start becoming a pain to add a new one of those for every single coffee shop I come across. The reduce() method reduces a JavaScript array into a single value. This is how it looks with the markers and popups loaded in. ![]() All it requires is an html file ( index.html) with the prerequisite CSS and JavaScript Leaflet files loading in:Ĭonst elMeson = L. Here is an example project on CodePen you can use. We will use reduce() to get the count of coffeeshops per Chicago neighborhood, and we'll use map() to pull data from an external JSON feed and show locations on the web map. Next goal is to use reduce() and map() in a real world example (the map) to simplify and make our code more efficient and DRY ( Don't Repeat Yourself).A review of JavaScript Variables and Datatypes will have most of the JavaScript knowledge you'd need up to this point. Basic knowlegde of HTML, CSS, and JavaScript.Here's the final map project that I created: Cafétographyįor this article, you can either create your own web map for something in your own neighborhood or the world that you would like to track, or you can simply view my examples of map(), filter() and reduce(). For this project, I decided to use Leaflet, a JavaScript library for interactive maps. On another occasion, I used Google Maps API to map out multiple store locations for restaurant concepts at my last job. we have access to the array's previous value apart from its current value and index. ![]() The difference is: as the name suggests it reduces the number of values in an array to one. After I accidentally visited one I didn't like very much but forgot about, I thought it might be a fun little project to map out all the cafes I write at in a web map. It's an ES5 method in JavaScript like for.each and map which we can use with arrays. Recently, I've been exploring Chicago and visiting various local coffeeshops to write with a gentle, pleasant ambiance, à la J.K. There are some JavaScript/ES6 concepts that are hard to grasp as just standalone snippets without seeing how they work as a piece of a bigger project, so I'm going to cover an example of how I used them in this article. We map through the users and then on each user we do a reduce and form a new object ( newObj) and then check for website key, if its a website we return the previously formed newObj, if not then we do a spread operator and add the required key to obj and finally, return newObj.I don't know about you, but it doesn't help me very much to peruse through endless examples of foo and bar to try to figure out how to use a feature of a programming language. ![]() Map // definition collection.map((currentValue, index) => )) Let’s start the real action with most used Javascript function for FP.
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