how to duplicate array javascript code example

Example 1: javascript copy an array

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

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

Example 2: assign array to another array javascript

var ar = ["apple","banana","canaple"];
var bar = Array.from(ar);
alert(bar[1]); // alerts 'banana'

// Notes: this is for in In ES6, works for an object of arrays too!

Example 3: count duplicates 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) { count[i] = (count[i]||0) + 1;});
console.log(count);

Example 4: js find duplicates in array

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' ]