[рони]

eLDeR,

document.addEventListener('DOMContentLoaded', function () {
	let codeinpit = document.querySelector('#promo');
	let price = document.getElementById('price');
    let timer;
	codeinpit.oninput = function () {
            window.clearTimeout(timer);
			let code = this.value;
			function wait() {
				const request = new XMLHttpRequest();
				const url = "../action/code.php?code=" + code;
				request.open('GET', url);
				request.setRequestHeader('Content-Type', 'application/x-www-form-url');
				request.addEventListener("readystatechange", () => {
					if (request.readyState === 4 && request.status === 200) {
						console.log( request.responseText );
					}
				});
				request.send();
//				price.innerHTML = code;
			}
			timer = setTimeout(wait, 3000);
		}
});