JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" />

JavaScript

var input = document.querySelector('input');
var oldVal = '';
input.addEventListener('keyup', function(){
    var parts = this.value.split('.');
    if (parts && parts[1] && parts[1].length > 3) this.value = oldVal;
    oldVal = this.value;
});