JSFiddle - React, Tailwind, and code Playground
HTML
<script type="text/javascript">
function kCap(iO){
iO.value = iO.value.replace(/([\wöçşğüıİ])/gi,
function(a, b){return b.replace("I","ı").toLowerCase()}).replace(/(^[a-zöçşğüı]|[\s|\.][a-zöçşğüı])/g,
function(c, d){return d.replace("i","İ").toUpperCase()});
}
</script>
<input type="text" value="" size="50" id="metin" onblur="kCap(this);" />