how to duplicate an array in JS code example

Example 1: js array clone

let clone = [...myArray]

Example 2: javascript copy array

var numbers = [1,2,3,4,5];
var newNumbers = Object.assign([], numbers);

Example 3: javascript duplicate an array

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

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

Example 4: javascript find duplicate in array

// JavaScript - finds if there is duplicate in an array. 
// Returns True or False.

const isThereADuplicate = function(arrayOfNumbers) {
    // Create an empty associative array or hash. 
    // 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 hash is 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;
        } else {
            return true;
        }
    }
    return false;
}

Example 5: duplicate numbers in an array javascript

[1, 1, 2, 2, 3].filter((element, index, array) => array.indexOf(element) !== index) // [1, 2]