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Learn how to use Higher Order FunctionsA Map, Filter, Reduce FundamentalsAll the functions are part of the JavaScript const arr = [1, 2, 3]arr.map() When we are using
map → Executes a function on each element of an arrayEvery element of the array is passed to the callback function and returns a new array with the same length. When to use Example 1 : var numbers= [1,2,3,4,5];var doubled = numbers.map(n => n * 2);doubled; // [2,4,6,8,10] filter → Remove items which don’t satisfy a conditionEvery element of the array is passed to the callback function. On each iteration, if the callback returns var numbers = [1,2,3,4,5];var greaterThan2 = numbers.filter(n => n > 2);greaterThan2; // [3,4,5] Reduce → Creates a single value from elements of ArrayWhile using Example 1: Sum of numbers var numbers = [1,2,3,4,5];var initialVal = 0;let result=numbers.reduce((accu, val) => val + accu , initialVal);console.log(result) // 15 Example 2: Creating an array of objects from user names Real-world exampleLet’s create a real-world practical example: Conducting an Interview
Join your hand🖐 with me Javascript Jeep🚙💨. Buy me a coffee Learn how Array.map and Array.filter work by writing them yourselfThis article is for those who have written a This has been taken from Step Up Your JS: A Comprehensive Guide to Intermediate JavaScript, my online course. Feel free to view it there for interactive versions of the code samples. Array.map
for-loopvar originalArr = [1, 2, 3, 4, 5]; Simple enough. Let’s
abstract this loop into its own function so that we can turn any array we like into a new array with each element multiplied by 3. In other words, we’re trying to write a function that will take in an any array ( Multiply by threevar originalArr = [1, 2, 3, 4, 5];function multiplyByThree(arr) { Beautiful. Now we can pass any array into var originalArr = [1, 2, 3, 4, 5];function timesThree(item) { This block does the same exact thing as the one before it. It just takes one piece out and turns it into its own function. What if we wanted to multiply all items in an array by 5? or 10? Would we want to make a new looping function for each of those? No, not at all. That would be tedious and repetitive. Multiply by anythingLet’s change the We’re turning this: function multiplyByThree(arr) { Into this. function multiply(arr, multiplyFunction) { We’ve renamed the function and given it an extra argument to take in. That argument itself will be a function (commonly referred to as a callback). Now, we’re passing a function in to var originalArr = [1, 2, 3, 4, 5];function timesThree(item) { We’re giving our var originalArr = [1, 2, 3, 4, 5];function timesFive(item) { It’s as simple as swapping out the MapLet’s make function multiply(arr, multiplyFunction) { Into this. function map(arr, transform) { Look closely at the bold and see what we changed between the We can pass in any function we want to function makeUpperCase(str) { We’ve effectively just written Using Array.mapHow does the function func(item) { Using the native function func(item) { That’s pretty much it. You’ve written More Array.map argumentsThere’s a key difference we’ve skipped over. function logItem(item) { This allows you to use the index and the original array inside your transformation function if you choose. For example, say we want to turn an array of items into a numbered shopping list. We’d want to use the index: function multiplyByIndex(item, index) { Our complete function map(arr, transform) { This short function is the essence of Lastly, you can also write a function directly in the var arr = [1, 2, 3, 4, 5];var arrTimesThree = arr.map(function(item) { Done. Phew. Array.filterThe idea here is similar to Array.map, except instead of transforming individual values, we want to filter existing values. Without any functions (besides for-loopvar arr = [2, 4, 6, 8, 10]; Let’s abstract this to a function so we can remove values below 5 in any array. function filterLessThanFive(arr) { Let’s make it so we can filter out all values below any arbitrary value. function isGreaterThan5(item) { → Abstracting out the filtering functionality function filterBelow(arr, greaterThan) { → Filtering out anything below 5, using filterBelow function isGreaterThan5(item) { → Filtering out anything below 7, using filterBelow function isGreaterThan7(item) { filterSo we have a function function filterBelow(arr, greaterThan) { Let’s rename it. function filter(arr, testFunction) { And we’ve written var arr = ['abc', 'def', 'ghijkl', 'mnopuv'];function longerThanThree(str) { Again, function func(item, index, arr) { So we should make our function do the same. function filter(arr, testFunction) { Wow. That’s it. You’ve learned how to use and write NotesIf there’s interest in covering If you liked this, please press the heart and feel free to check out my other publications.
How do you use map and reduce together?JavaScript reduce method. reduce examples and uses. Using reduce and map() together.. They are dynamic.. They can be sparse or dense.. They are mutable.. They have methods and properties to make organization convenient.. What is difference between map and filter in JavaScript?map creates a new array by transforming every element in an array individually. filter creates a new array by removing elements that don't belong.
What is filter () map () and reduce ()?Map, Filter, and Reduce are paradigms of functional programming. They allow the programmer (you) to write simpler, shorter code, without neccessarily needing to bother about intricacies like loops and branching.
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