If you want to accept only uppercase input in an HTML element such as a input text or a text area, even if the user enters the text in lowercase you want it to be converted and captured in all capital letters you can do so by adding the attribute text-transform: uppercase to the style of the the element,
The property text-transformation is available since CSS1 and support all browsers: Chrome, Internet Explorer, Edge, Safari and Firefox.
Syntax: text-transform: uppercase
As you can see in the below demo, even when I do not press shift key or caps button on, all the characters are force captured in uppercase in the text field.

<!DOCTYPE html>
<html>
<body>
<input type="text "id="message" style="text-transform: uppercase" />
</body>
</html>
This will work with textarea as well,
<textarea style="text-transform: uppercase"></textarea>
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