cookies - run javascript only once -

i need run javascript once, save cookies, then, when try execute function, check if cookies saved, if so, don't trigger function.

i'm sure script has error because doesn't need :

var prom = getcookie('prom'); if (prom === null || prom === '0')  { if (document.getelementbyid('tst')){     var str=document.getelementbyid("tst").innerhtml;     var n=str.replace("login","logout");     document.getelementbyid("tst").innerhtml=n;     setcookie("prom",'1',1); } } 

html code script triggers change 'login' in 'logout'

<a href="login"  title="log in" class="login_button" id="tst">login</a></span> 

cookies script :

function setcookie(c_name, value, exdays) {     var exdate = new date();     if (exdays) exdate.setdate(exdate.getdate() + exdays);     var c_value = escape(value) + ((exdays) ? '; expires=' + exdate.toutcstring() : '');     document.cookie = c_name + "=" + c_value; }  function getcookie(name) {     var re = new regexp(name + "=([^;,]+)");     var value = re.exec(document.cookie);     return (value !== null) ? unescape(value[1]) : null; } 

jsfiddle test if http://jsfiddle.net/8yzap/11/

change

if (prom = '0'){ 

to

if (prom === '0'){ 

(of course, assuming getcookie , setcookie persist similar sessionstorage).