JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" placeholder="defaultText" class="input">

JavaScript

$(function(){
    var dft = 'DEFAULT - ';
    $('input.input').keyup(function(evt){
        /* Key up event to catch all keys, keypressed doesn't catch i.E. 
        backspace*/
        /* If input value is empty don't alter it, that keeps input clean */
        if($(this).val() != ''){
            /* attach value of input to variable to alter it in future */
            var txt = $(this).val();
            /* txt.replace removes already added default text to prevent infinite prepending */
            $(this).val(dft + txt.replace(dft, ''));
        }
    }).keydown(function(evt){
        /* Key down is to catch user before he deletes part of default text and remove whole for him. That keeps it clean in future. */
        if($(this).val() == dft){
            /* Set input empty when user's trying to delete default text */
            $(this).val('');
            /* blocks further parsing */
            return false;
        }
    });
});