JSFiddle - React, Tailwind, and code Playground

HTML

<input id="beLowerCase" type="Text" />

JavaScript

$("#beLowerCase").on('input', function(){
    
    var start = this.selectionStart,
        end = this.selectionEnd;
    
    this.value = this.value.toLowerCase();
    this.setSelectionRange(start, end);
});