debounce - функция задержки ввода

HTML

<div id="wrapper">
    <input id="input" type="text" placeholder="input something..." />
    <span id="target"></span>
</div>

JavaScript

function debounce(cb, interval, immediate) {
    var timeout;
    
    return function() {
        var context = this, args = arguments;
        var later = function() {
            timeout = null;
            if (!immediate) cb.apply(context, args);
        };          
    
        var callNow = immediate && !timeout;
    
        clearTimeout(timeout);
        timeout = setTimeout(later, interval);
    
        if (callNow) cb.apply(context, args);
    };
};
    
function keyPressCallback() {
    var target = document.getElementById('target');
    var input = document.getElementById('input');
    
    target.textContent = input.value;
}

document.getElementById('input').onkeypress = debounce(keyPressCallback, 400);