How to create a map (javascript maps object)
var map1 = new Map([[1 , 2], [3 ,4 ] ,[5, 6]]); console.log(map1) ; OUT Put 0: {1 => 2} key: 1 value: 2 1: {3 => 4} key: 3 value: 4 2: {5 => 6} key: 5 value: 6 var map2 = new Map([["firstname" ,"Avy"], ["lastname", "Jai"], ["website", "askavy"]] ); console.log(map2) ; out put Map(3) {"firstname" => "Avy", "lastname" => "Jai", "website" => "askavy"} 0: {"firstname" => "Avy"} 1: {"lastname" => "Jai"} 2: {"website" => "askavy"} How to use Map.set
var map3 = new Map(); map3.set('key', 'value'); console.log(map3) ; OutPut Map(1) {"key" => "value"} 0: {"key" => "value"} How to use map.get
var map3 = new Map(); map3.set('key', 'value'); console.log(map3.get('key')) ; OutPut Value how to use map.has
map.has return true if key found in array
var map3 = new Map(); map3.set('key', 'value'); console.log(map3.has('key')) ; OutPut true js arr map
var arr = [1, 2, 3, 4, 5, 6]; var newArr = arr.map(function (val, index) { return { key: index, value: val }; }); console.log(newArr); Output 0: {key: 0, value: 1} 1: {key: 1, value: 2} 2: {key: 2, value: 3} 3: {key: 3, value: 4} 4: {key: 4, value: 5} 5: {key: 5, value: 6} javascript map array of objects
var arr = [ { id: 1, name: "Avy", }, { id: 2, name: "Mark", }, ]; var result = arr.map((person) => ({ value: person.id, text: person.name, })); --- result is a array that have following values 0: {value: 1, text: "Avy"} 1: {value: 2, text: "Mark"} reformat objects javascript map array of objects
var personsArr = [ { id: 1, firstName: "Mark", lastName: "Selva", }, { id: 2, firstName: "Avy", lastName: "Jai", }, { id: 3, firstName: "Aaj", lastName: "kaal", }, ]; var newObj = {}; let fullname = personsArr.map((person) => { newObj = person.firstName + " " + person.lastName; return newObj; }); console.log(fullname); OutPut 0: "Mark Selva" 1: "Avy Jai" 2: "Aaj kaal" javascript map index
const ArrayList = ["A", "B", "C", "D", "E"]; ArrayList.map((currentElement, index) => { console.log("The current iteration is: " + index + " The current element is: " + currentElement); }); Output The current iteration is: 0 The current element is: A The current iteration is: 1 The current element is: B The current iteration is: 2 The current element is: C The current iteration is: 3 The current element is: D The current iteration is: 4 The current element is: E javascript map reduce
The reduce() method reduces an array of values down to just one value, reducer has mainly 2 arguments first is an accumulator and second on is currentValue (currentValue is the value of array element)
there is four arguments of reduce function
accumulator – the returned value of the previous iteration
currentValue – the current item in the array
index – the index of the current item
array – the original array on which reduce was called
const numbers = [1, 2, 3, 4]; const sum = numbers.reduce(function (accumulator, currentValue) { console.log( "accumulator = " + accumulator + " currentValue = " + currentValue ); return accumulator + currentValue; }, 0); // 0 means accumulator value is set to 0 and currentValue is 1 Result accumulator = 0 currentValue = 1 accumulator = 1 currentValue = 2 accumulator = 3 currentValue = 3 accumulator = 6 currentValue = 4 const numbers = [1, 2, 3, 4]; const sum = numbers.reduce(function (accumulator, currentValue) { console.log( "accumulator = " + accumulator + " currentValue = " + currentValue ); return accumulator + currentValue; }); // accumulator is set 1 and currentValue is set to 2 Result accumulator = 1 currentValue = 2 accumulator = 3 currentValue = 3 accumulator = 6 currentValue = 4 How to find the sum of an array of numbers
const numbers = [1, 2, 3, 4]; const sum = numbers.reduce(function (accumulator, currentValue) { return accumulator + currentValue; }); console.log(sum); // Result 10 ES6 Version
const numbers = [1, 2, 3, 4]; const sum = numbers.reduce((accumulator, currentValue) => { return accumulator + currentValue; }); console.log(sum); How to skip over an element in .map()
const numbers = [1, 2, 3, 4]; // skipping 3rd element const sum = numbers.reduce((accumulator, currentValue) => { if (currentValue == 3) { return false; // skip } else { return accumulator + currentValue; } }); console.log(sum); // result 4 
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