javascript get duplicates in array

                                    function findDuplicates(arr) {
	const duplicates = new Set()
  
  return arr.filter(item => {
  	if (duplicates.has(item)) {
    	return true
    }
    duplicates.add(item)
    return false
  })
}

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

const count = names =>
  names.reduce((a, b) => ({ ...a,
    [b]: (a[b] || 0) + 1
  }), {}) // don't forget to initialize the accumulator

const duplicates = dict =>
  Object.keys(dict).filter((a) => dict[a] > 1)

console.log(count(names)) // { Mike: 1, Matt: 1, Nancy: 2, Adam: 1, Jenny: 1, Carl: 1 }
console.log(duplicates(count(names))) // [ 'Nancy' ]

                                    let arr =["a","b","c"];
// ES6 way
const duplicate = [...arr];

// older method
const duplicate = Array.from(arr);

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

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

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

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

                                    function getDuplicateArrayElements(arr){<br/>    var sorted_arr = arr.slice().sort();<br/>    var results = [];<br/>    for (var i = 0; i &lt; sorted_arr.length - 1; i++) {<br/>        if (sorted_arr[i + 1] === sorted_arr[i]) {<br/>            results.push(sorted_arr[i]);<br/>        }<br/>    }<br/>    return results;<br/>}<br/><br/>var colors = [&quot;red&quot;,&quot;orange&quot;,&quot;blue&quot;,&quot;green&quot;,&quot;red&quot;,&quot;blue&quot;];<br/>var duplicateColors= getDuplicateArrayElements(colors);//[&quot;blue&quot;, &quot;red&quot;]