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How to Merge Two Arrays and Remove Duplicate Items in JavaScript?

JavaScript – Check if Two Arrays are Disjoint

Last Updated : 17 Nov, 2024

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Here are some approaches to determine if two arrays share any common item in JavaScript

1. Using Loops – Simple

The simplest way to find common items is by using nested loops to compare each item in one array (a1) with every item in the second array (a2). This is great for smaller arrays, but less efficient for larger datasets.

JavaScript

const a1 = [1, 2, 3]; const a2 = [4, 5, 3];  let hasCommonItem = false; for (let i = 0; i < a1.length; i++) {     for (let j = 0; j < a2.length; j++) {         if (a1[i] === a2[j]) {             hasCommonItem = true;             break;         }     } }  console.log(hasCommonItem);

Output

true

3. Using Set and some() – Efficient

For larger arrays, converting one array (a2) into a Set and using some() to check items in a1 against the Set reduces time complexity as Set provides constant-time lookups.

JavaScript

const a1 = [1, 2, 3]; const a2 = [4, 5, 3];  const set = new Set(a2); const hasCommonItem = a1.some(item => set.has(item)); console.log(hasCommonItem);

Output

true

2. Using some() and includes()

The some() method, when combined with includes(), provides a more simpler way to check if any item in a1 exists in a2.

JavaScript

const a1 = [1, 2, 3]; const a2 = [4, 5, 3];  const hasCommonItem = a1.some(item => a2.includes(item)); console.log(hasCommonItem);

Output

true

4. Using filter() to Find Common Items

The filter() method can be used to get an array of items present in both a1 and a2. If the result has elements, then a1 and a2 share common items.

JavaScript

const a1 = [1, 2, 3]; const a2 = [4, 3, 5];  const commonItems = a1.filter(item => a2.includes(item)); console.log(commonItems); console.log(commonItems.length > 0);

Output

[ 3 ] true

5. Using Set Intersection

Creating a Set intersection is efficient when both arrays are converted into Sets. We then filter items from a1 that are in a2, resulting in the intersection of the two sets.

JavaScript

const a1 = [1, 2, 3]; const a2 = [3, 4, 5];  const intersection = new Set(a1.filter(item => new Set(a2).has(item))); console.log(intersection.size > 0);

Output

true

Importance of Finding Common Items Between Arrays

Finding common items between arrays is crucial for

Data Comparison: Quickly verifying overlaps between data lists.
Conditional Processing: Executing code based on shared elements.
Performance: Optimizing large data comparisons by choosing efficient methods like Set.

How to Merge Two Arrays and Remove Duplicate Items in JavaScript?

anuupadhyay

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Article Tags :

JavaScript
Web Technologies
javascript-array
JavaScript-DSA
JavaScript-Questions

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