gistfile1.js

function getXHR() {
	var xhr = null;
	
	if (window.XMLHttpRequest || window.ActiveXObject) {
		if (window.ActiveXObject) {
			try {
				xhr = new ActiveXObject("Msxml2.XMLHTTP");
			} catch(e) {
				xhr = new ActiveXObject("Microsoft.XMLHTTP");
			}
		} else {
			xhr = new XMLHttpRequest(); 
		}
	} else {
		alert("Impossible d'utiliser XMLHttpRequest sur votre navigateur.");
		return null;
	}
	
	return xhr;
}

function update() {
    var liste = document.forms[0].elements['liste'];
    var caseA = document.forms[0].elements['A'];
    var caseB = document.forms[0].elements['V'];
    var caseC = document.forms[0].elements['C'];


	/* Requête AJAX */
	xhr.onreadystatechange = function() {
		if(xhr.readyState == 4 && (xhr.status == 0 || xhr.status = 200)) {
			/* Affichage dans l'input */
			var finalInput = document.forms[0].elements['final'];
			var chaine = "";

			chaine += liste.value;
		
			if(caseA.checked) {
				chaine += " A";
			}

			if(caseB.checked) {
				chaine += " B";
			}
			if(caseC.checked) {
				chaine += " C";
			}

			finalInput.value = chaine;
		}
	};
	
	xhr.open('POST','/script.php', true);
	xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
	xhr.send('listeValue='+liste.value+'&case_a='+caseA.checked+'&case_b='+caseB.checked+'&case_c='+caseC.checked);
}