Add Check Classes On A DOM Element as a javascript til

README.md

@@ -9,7 +9,7 @@ and pairing with smart people at Hashrocket.
 
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-_926 TILs and counting..._
+_927 TILs and counting..._
 
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@@ -296,6 +296,7 @@ _926 TILs and counting..._
 - [Accessing Arguments To A Function](javascript/accessing-arguments-to-a-function.md)
 - [Basic Date Formatting Without A Library](javascript/basic-date-formatting-without-a-library.md)
 - [Character Codes from Keyboard Listeners](javascript/character-codes-from-keyboard-listeners.md)
+- [Check Classes On A DOM Element](javascript/check-classes-on-a-dom-element.md)
 - [Check If Something Is An Array](javascript/check-if-something-is-an-array.md)
 - [Check The Password Confirmation With Yup](javascript/check-the-password-confirmation-with-yup.md)
 - [Computed Property Names In ES6](javascript/computed-property-names-in-es6.md)

javascript/check-classes-on-a-dom-element.md

@@ -0,0 +1,29 @@
+# Check Classes On A DOM Element
+
+You can use the [`classList`
+property](https://developer.mozilla.org/en-US/docs/Web/API/Element/classList)
+to check what classes have been assigned to a DOM element.
+
+Assuming the following DOM element:
+
+```html
+<div id="auth-modal" class="modal hidden">...</div>
+```
+
+Once you get a handle on that element, using your preferred method (e.g.
+[`Document.getElementById`](https://developer.mozilla.org/en-US/docs/Web/API/Document/getElementById)),
+you can start inspecting the class list:
+
+```javascript
+> element.classList.contains("modal")
+true
+
+> element.classList.contains("hidden")
+true
+
+> element.classList.contains("taco")
+false
+
+> element.classList.toString()
+"modal hidden"
+```