Remove duplicates from an array using indexOf() and filter() methods

There are many ways to remove duplicates from array in JavaScript but today I will use indexOf and filter methods!

The indexOf() method returns the index of the first occurrence of an element in an array. For example:

let chars = ['A', 'B', 'A', 'C', 'B'];
chars.indexOf('B');

Output: 1

To remove the duplicates, you use the filter() method to include only elements whose indexes match their indexOf values:

const arr = ['A', 'B', 'A', 'C', 'B'];
const uniqueArr = arr.filter((c, index) => {
    return arr.indexOf(c) === index;
});
console.log(uniqueArr);

Output: [ 'A', 'B', 'C' ]

To find the duplicate values, you just need to reverse the condition:

const arr = ['A', 'B', 'A', 'C', 'B'];
const uniqueArr = arr.filter((c, index) => {
    return arr.indexOf(c) !== index;
});
console.log(uniqueArr);

Output: [ 'A', 'B' ]

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