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Javascript ES6 (ES0215) .map(), .reduce(), .filter() usage examples.
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| // FILTER | |
| /* | |
| If i already have an array but i only want to have items in the array that match certain criteria, use the filter. | |
| Quando eu já tenho um array e quero apenas itens no novo array que correspondem a uma condição, use filter. | |
| */ | |
| // GET JUST EVEN NUMBERS | |
| let arr = [-200, -163, -26, -4, 0, 7, 76]; | |
| let evens = arr.filter(function(x) { | |
| return x % 2 === 0; | |
| }); | |
| // Arrow function | |
| let evens = arr.filter(x => x % 2 === 0); | |
| // Using external function | |
| function isEven(value) { | |
| return value % 2 === 0; | |
| } | |
| let evens = arr.filter(isEven); | |
| // MAP | |
| /* | |
| If i already have an array and i want to do the exact same operation on each of the elements in the array and return the same amount of items in the array, use the map. | |
| Se eu já tenho um array e quero fazer uma mesma operação em cada elemento do array e retorna a mesma quantidade de itens do array, use map. | |
| */ | |
| // MULTIPLY ALL ARRAY VALUES | |
| let arr1 = [1, 2, 3, 4]; | |
| let mult = arr1.map(function (value){ | |
| return value * 3; | |
| }); | |
| // Arrow function | |
| let mult = arr1.map(value => value * 3); | |
| // REDUCE | |
| /* | |
| If i already have an array, but i want to use the values in that array to create something completely new, use the reduce. | |
| Se eu já tenho um array, mas eu quero usar os valores deste array para criar algo completamente novo, use reduce. | |
| */ | |
| // SUM UP THE POPULATION OF EVERY COUNTRY EXCEPT CHINA? | |
| let data = [ | |
| { | |
| country: 'China', | |
| pop: 1409517397, | |
| }, | |
| { | |
| country: 'India', | |
| pop: 1339180127, | |
| }, | |
| { | |
| country: 'USA', | |
| pop: 324459463, | |
| }, | |
| { | |
| country: 'Indonesia', | |
| pop: 263991379, | |
| } | |
| ]; | |
| let sum = data.reduce((acc, val) => { | |
| return val.country == 'China' ? acc : acc + val.pop; | |
| }, 0); | |
| // SUM TOTAL PILOTS YEARS | |
| let pilots = [ | |
| { | |
| id: 10, | |
| name: "Poe Dameron", | |
| years: 14, | |
| }, | |
| { | |
| id: 2, | |
| name: "Temmin 'Snap' Wexley", | |
| years: 30, | |
| }, | |
| { | |
| id: 41, | |
| name: "Tallissan Lintra", | |
| years: 16, | |
| }, | |
| { | |
| id: 99, | |
| name: "Ello Asty", | |
| years: 22, | |
| } | |
| ]; | |
| let alYears = pilots.reduce((acc, pilot) => acc + pilot.years, 0); | |
| /* | |
| REFERENCES | |
| DESCRIPTIONS: https://hackernoon.com/understanding-map-filter-and-reduce-in-javascript-5df1c7eee464 | |
| FILTER EVEN NUMBERS EXAMPLE: https://stackoverflow.com/a/51876403 | |
| REDUCE POPULATION EXAMPLE: https://codeburst.io/learn-understand-javascripts-reduce-function-b2b0406efbdc | |
| REDUCE PILOTS YEARS EXAMPLE: https://medium.com/poka-techblog/simplify-your-javascript-use-map-reduce-and-filter-bd02c593cc2d | |
| */ |
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