JSFiddle - React, Tailwind, and code Playground

by Alexis LĂłpez Espinoza

HTML

<input type="text" id="foo" value="+569" autofocus />

JavaScript

var foo = document.querySelector("#foo");

foo.addEventListener("keydown", function(event){
	if ((event.which == 8 && this.value.length < 5) || (event.which == 46 && this.selectionStart < 4) || (event.which != 37 && event.which != 39 && this.selectionStart < 4)){
		event.preventDefault();
	}
}, false);

foo.addEventListener("input", function(){
	this.value = this.value.replace(/[^0-9\+]/g, "");
	this.value = this.value.substr(0, 4) + this.value.substr(4).replace(/\++/g, "");
}, false);