JavaScript - remove duplicates from array

In this short article, we would like to show how to remove duplicated items in an array in JavaScript.

Quick solution:

// ONLINE-RUNNER:browser;

const array = [1, 2, 3, 1, 1, 2, 2, 3, 3];
const result = array.filter((item, index, array) => array.indexOf(item) === index);

console.log(JSON.stringify(result)); // [1,2,3]

Reusable function example

The below approaches reduce the number of iterations.

1. Set based approach

// ONLINE-RUNNER:browser;

const removeDuplicates = (array) => {
  	const result = [];
	const blocker = new Set(); // prevents against item duplication
  	for (const item of array) {
    	if (blocker.has(item)) {
            continue;
        }
        blocker.add(item);
        result.push(item);
    }
  	return result;
};


// Usage example:

const array = [1, 2, 3, 1, 1, 2, 2, 3, 3];
const uniqueItems = removeDuplicates(array);

console.log(JSON.stringify(uniqueItems)); // [1,2,3]

2. Simple types approach

This solution should be used when each item has the same type in the array, and the type is one of: boolean, number or string.

// ONLINE-RUNNER:browser;

const removeDuplicates = (array) => {
  	const result = [];
	const blocker = {}; // prevents against item duplication
  	for (const item of array) {
    	if (blocker.hasOwnProperty(item)) {
        	continue;
        }
      	blocker[item] = true;
      	result.push(item);
    }
  	return result;
};

// Usage example:

const array = [1, 2, 3, 1, 1, 2, 2, 3, 3];
const uniqueItems = removeDuplicates(array);

console.log(JSON.stringify(uniqueItems)); // [1,2,3]

References

• Remove duplicated array items in JavaScript