Check if Arrays contain Common Elements in JavaScript

Check if Arrays contain common Elements - includes #

To check if two arrays in JavaScript contain common elements:

1. Use the Array.some method on the first array, passing it a function
2. The function should return whether the element is included in the second array
3. If there is at least 1 common element, Array.some will return true

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// Not Supported in IE 6-11
const arr1 = ['pizza', 'cake', 'cola'];
const arr2 = ['pizza', 'beer'];

const contains = arr1.some(element => {
  return arr2.includes(element);
});

console.log(contains); // 👉️ true

The function we passed to the Array.some method is called for each element of the array.

The arrays in the example have a common element, therefore the Array.includes method returns true, causing the Array.some method to also return true.

Check if Arrays contain common Elements - indexOf #

We can also check if two javascript arrays contain common elements, using Array.indexOf, instead of Array.includes.

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// Supported in IE 9-11
const arr1 = ['pizza', 'cake', 'cola'];
const arr2 = ['pizza', 'beer'];

const contains = arr1.some(element => {
  return arr2.indexOf(element) !== -1;
});

console.log(contains); // 👉️ true

If the arrays have a common element, then Array.indexOf will return the element's index, otherwise it returns -1.

In the code example, there is a common element between the arrays, therefore the callback function returns true and the Array.some method also returns true.