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Case-insensitive substring search

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.

const includesCaseInsensitive = (str, searchString) =>
  new RegExp(searchString, 'i').test(str);

includesCaseInsensitive('Blue Whale', 'blue'); // true

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