function emailCheck (emailStr) {

	var myEMailIsValid = true;
	var myAtSymbolAt = emailStr.indexOf('@');
	var myLastDotAt = emailStr.lastIndexOf('.');
	var mySpaceAt = emailStr.indexOf(' ');
	var myLength = emailStr.length;
	
	// at least one @ must be present and not before position 2
	// @yellow.com : NOT valid
	// x@yellow.com : VALID
	
	if (myAtSymbolAt < 1 ) {
		myEMailIsValid = false;
	}
	
	
	// at least one . (dot) afer the @ is required
	// x@yellow : NOT valid
	// x.y@yellow : NOT valid
	// x@yellow.org : VALID
	
	if (myLastDotAt < myAtSymbolAt) {
		myEMailIsValid = false;
	}
	
	// at least two characters [com, uk, fr, ...] must occur after the last . (dot)
	// x.y@yellow. : NOT valid
	// x.y@yellow.a : NOT valid
	// x.y@yellow.ca : VALID
	 
	if (myLength - myLastDotAt <= 2) {
		myEMailIsValid = false;
	}
	
	// no empty space " " is permitted (one may trim the email)
	// x.y@yell ow.com : NOT valid
	
	if (mySpaceAt != -1) {
		myEMailIsValid = false
	}
		
	if (myEMailIsValid == true) {
		return true;
	}
	else {
		return false;
	}

}

function check_form(){
	if(document.getElementById('nom').value == '') {
		alert("Veuillez entrer votre nom !");
		return false;
	}
	if(document.getElementById('prenom').value == '') {
		alert("Veuillez entrer votre prenom !");
		return false;
	}
	if(document.getElementById('texte').value == '') {
		alert("Veuillez entrer votre message !");
		return false;
	}
	if(!emailCheck(document.getElementById('email').value)){
		alert("L'adresse mail n'est pas valide !");
		return false;
	}
	return true;
}