comprobar duplicado en array ejemplo de código javascript

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Ejemplo 1: contar duplicados array js

uniqueCount =["a","b","c","d","d","e","a","b","c","f","g","h","h","h","e","a"];
var count =;
uniqueCount.forEach(function(i)0)+1;);
console.log(count);

Ejemplo 2: cómo obtener valores duplicados de array en javascript

var array =[1,2,2,3,3,4,5,6,2,3,7,8,5,22,1,2,511,12,50,22];

console.log([...new Set(
  array.filter((value, index, self)=> self.indexOf(value)!== index))]);

Ejemplo 3: cómo obtener valores duplicados de array en javascript

var names =['Mike','Matt','Nancy','Adam','Jenny','Nancy','Carl']

var uniq = names
  .map((name)=>return
      count:1,
      name: name
    ).reduce((a, b)=>0)+ b.count
    return a
  ,)

var duplicates = Object.keys(uniq).filter((a)=> uniq[a]>1)

console.log(duplicates)//['Nancy']

Ejemplo 4: javascript encuentra duplicado en array

// JavaScript - finds if there is duplicate in an array.// Returns TrueorFalse.

const isThereADuplicate = function(arrayOfNumbers)// Create an empty associative array orhash.// This is preferred,
    let counts =;//// but this also works. Comment in below and comment out above if you want to try.// let counts =[];for(var i =0; i <= arrayOfNumbers.length; i++)// As the arrayOfNumbers is being iterated through,// the counts hashis being populated.// Each value in the array becomes a key in the hash.// The value assignment of 1,is there to complete the hash structure.// Once the key exists, meaning there is a duplicate,return true.// If there are no duplicates, the if block completes and returns false.if(counts[arrayOfNumbers[i]]=== undefined)
            counts[arrayOfNumbers[i]]=1;elsereturn true;return false;

Ejemplo 5: busque duplicados en array javascript

[1,2,2,4,3,4].filter((e, i, a)=> a.indexOf(e)!== i)//[2,4]

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