How to use javascript to check if class that starts with (classname__) exists?

Question

In the snippet below, I'm using the contains() method to check if a class that starts with banner__ exists in the document. If I define the class explicitly, then I can get a true response. But there are various classes that could exist in the document that start with banner__ .

How do I check if a class that starts with banner__ exists?

 const banner = document.querySelector('.banner'); const isBanner = banner.classList.contains('banner__'); if (isBanner) { console.log('Exists') } else { console.log('Does not exist') }

 <div class="banner banner__holiday">Banner</div>

Answer 1

Convert the class list to an array, then use .some() to test if any of them begin with what you want.

 const banner = document.querySelector('.banner'); const isBanner = Array.from(banner.classList).some(c => c.startsWith('banner__')); if (isBanner) { console.log('Exists') } else { console.log('Does not exist') }

 <div class="banner banner__holiday">Banner</div>