JSFiddle - React, Tailwind, and code Playground

HTML

<textarea></textarea>
<button>Submit</button>
<p></p>

JavaScript

$('button').click(function(){
    var links = $('textarea').val().split('\n');
    
    for(var i = 0; i < links.length; i++) {
        if(links[i].substring(0, 7) !== 'http://') {
            $('p').text('Error!');
            return false;
        }
    }
    
    return true;
});