How to remove duplicate elements from JavaScript Array ?

In this article, we will discuss the methods to remove duplicate elements from a Javascript array. There are various methods to remove duplicates in the array. We will discuss the most common four ways :

• filter() method
• set() method
• reduce() method
• indexOf() method
• Javascript forEach() Method

Below all the methods are described with proper examples:

Javascript filter() Method: The filter() method creates a new array of elements that pass the condition we provide. It will include only those elements for which true is returned. We can remove duplicate values from the array by simply adjusting our condition.

Example: In this example, we will see the use of the filter() method.

Javascript

let arr = ["apple", "mango", "apple",
          "orange", "mango", "mango"];

function removeDuplicates(arr) {
    return arr.filter((item,
        index) => arr.indexOf(item) === index);
}

console.log(removeDuplicates(arr));

Output:

["apple", "mango", "orange"]

Javascript set() Method: This method sets a new object type with ES6 (ES2015) that allows you to create collections of unique values.

Example: In this example, we will see the use of the set() method.

Javascript

let arr = ["apple", "mango", "apple",
          "orange", "mango", "mango"];

function removeDuplicates(arr) {
    return [...new Set(arr)];
}

console.log(removeDuplicates(arr));

Output:

["apple", "mango", "orange"]

Javascript forEach() Method: By using the forEach() method, we can iterate over the elements in the array, and we will push into the new array if it doesn’t exist in the array.

Example: In this example, we will see the use of the forEach() method.

Javascript

let arr = ["apple", "mango",
          "apple", "orange", "mango", "mango"];

function removeDuplicates(arr) {
    let unique = [];
    arr.forEach(element => {
        if (!unique.includes(element)) {
            unique.push(element);
        }
    });
    return unique;
}
console.log(removeDuplicates(arr));

Output:

["apple", "mango", "orange"]

Javascript reduce() Method: The reduce() method is used to reduce the elements of the array and combine them into a final array based on some reducer function that you pass.

Example: In this example, we will see the use of the reduce() method.

Javascript

let arr = ["apple", "mango",
          "apple", "orange", "mango", "mango"];

function removeDuplicates(arr) {
    let unique = arr.reduce(function (acc, curr) {
        if (!acc.includes(curr))
            acc.push(curr);
        return acc;
    }, []);
    return unique;
}
console.log(removeDuplicates(arr));

Output:

["apple", "mango", "orange"]

Javascript indexOf() Method: The indexOf() method is used to find the first index of occurrence of an array element. we can iterate over the elements in the array, and we will push into the new array if it doesn’t exist in the resultant array. 

Example: In this example, we will see the use of the indexOf() method.

Javascript

let arr = ["apple", "mango",
          "apple", "orange", "mango", "mango"];

function removeDuplicates(arr) {
    let unique = [];
    for (i = 0; i < arr.length; i++) {
        if (unique.indexOf(arr[i]) === -1) {
            unique.push(arr[i]);
        }
    }
    return unique;
}
console.log(removeDuplicates(arr));

Output:

['apple', 'mango', 'orange']