Add includesCaseInsensitive

snippets/includesCaseInsensitive.md

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+---
+title: Case-insensitive substring search
+tags: string
+expertise: beginner
+author: chalarangelo
+cover: blog_images/cup-of-orange.jpg
+firstSeen: 2022-07-28T05:00:00-04:00
+---
+
+Checks if a string contains a substring, case-insensitive.
+
+- Use the `RegExp` constructor with the `'i'` flag to create a regular expression, that matches the given `searchString`, ignoring the case.
+- Use `RegExp.prototype.test()` to check if the string contains the substring.
+
+```js
+const includesCaseInsensitive = (str, searchString) =>
+  new RegExp(searchString, 'i').test(str);
+```
+
+```js
+includesCaseInsensitive('Blue Whale', 'blue'); // true
+```