September 28, 2021

How to Remove Duplicate Elements from Array in Javascript

By Krishnaa JavaScript Questions 0 Comments

In this tutorial, you will learn how to remove duplicate elements from array in javascript. Arrays generally act like a collection of items. The data type of those items could be similar or could be different.

The tutorial is mainly focused on the string type. The same technique can also work with number type but make sure you do not use toLowerCase() and toUpperCase() methods as shown in this tutorial since these methods are only available for strings.

There is no built-in method to remove duplicates items from an array so we have to use other built-in methods and loops in the right sequence to accomplish our goal.

In the following example, we have a global array of fruits. Initially, we will display all fruit names on the screen. Upon click of a button, we will remove duplicates fruit names and update our list. Please have a look over the code example and the steps given below.

HTML & CSS

We have 2 elements in the HTML file (button and ul).
The innerText for the button element is “Remove Duplicates”.
The ul element is empty as of now and we will populate it dynamically using javascript.
We have also included our javascript file script.js with a script tag at the bottom.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<body>
  
  <button>Remove Duplicates</button>
  <ul></ul>
  <script src="script.js"></script>
</body>
</html>

Javascript

We have a global variable fruits and it holds an array of strings.
We have the addFruits() method which will populate our ul element with list of fruit names.
In addFruits() method, we are simply looping through the fruits array and creating a template string with a bunch of li elements.
We are displaying that list in the ul element by using the innerHTML property.
We are calling the addFruits() method to display our initial fruits list.
We have selected the button element using the document.querySelector() method and attached the click event listener to it.

Case Sensitive Comparison

We are using the Set constructor to create a Set of fruits. By default, you cannot have duplicate items in a Set. We are storing our fruits Set in the mySet variable
We are using Array.from() method to convert Set into an array. We are assigning it back to the fruits variable.
We are calling the addFruits() method to update our fruits list.

Case Insensitive Comparison

We are using the map() method to loop through all items in the array. Inside the loop, we are using the toLowerCase() method to have all fruit names in the lowercase.
We are using the filter() method to remove duplicate items from the array. Inside the loop, we are simply using the indexOf() method to check if a certain item is already present or not.
We are again using the map() method to capitalize the first letter of each fruit name.
Inside the loop, we are using the index of 0 to get the first letter and then using the toUpperCase() method to capitalize it. We are using the slice() method to slice the string from index 1. We are joining the capitalized letter and sliced string by using the addition (+) operator.
We are calling the addFruits() method to update our fruits list.

let fruits = ['Apple', 'Orange', 'Kiwi', 'Grapes', 'Mango', 'kiwi', 'grapes'];

function addFruits(){
    let template = fruits.map(fruit => `<li>${fruit}</li>`).join('\n');
    document.querySelector('ul').innerHTML = template;
}

addFruits();

document.querySelector('button').addEventListener('click', () =>{
    /* let mySet = new Set(fruits);
    fruits = Array.from(mySet);
    addFruits(); */

    fruits = fruits.map(fruit => fruit.toLowerCase());
    fruits = fruits.filter((item, index) => fruits.indexOf(item) == index);
    fruits = fruits.map(fruit => fruit[0].toUpperCase() + fruit.slice(1));
    addFruits();
});

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