JSFiddle - React, Tailwind, and code Playground

HTML

Try to input www.myurl.com<br />
Try to input http://www.myurl.com<br />
Try to input https://www.myurl.com<br /><br />
URL INPUT:<br />
<input type="url" id="url_input" name="url_input" oninput="check_url()"/><br /><br />
<input type="button" value="Submit!!" />

JavaScript

//PUT THIS IN HEAD

function check_url(){
    //Get input value
    var elem = document.getElementById("url_input");
    var input_value = elem.value;
	//Set input value to lower case so HTTP or HtTp become http
	input_value = input_value.toLowerCase();
    
    //Check if string starts with http:// or https://
    var regExr = /^(http:|https:)\/\/.*$/m;
    
    //Test expression
    var result = regExr.test(input_value);
	
	//If http:// or https:// is not present add http:// before user input
    if (!result){
		var new_value = "http://"+input_value;
		elem.value=new_value;
    }
}