problem using some javascript codes in header

hello
im trying to add this javascript code to my header but its not working
im using graviti theme

var rotatingTextElement;
var rotatingText = new Array();
var ctr = 0;

function initRotateText() {
rotatingTextElement = document.getElementById("textToChange");
rotatingText[0] = rotatingTextElement.innerHTML; // store the content that's already on the page
rotatingText[1] = "<a href='<?php echo $long_link; ?>'>some words</a>";

setInterval(rotateText, 10000);
}
function rotateText() {
ctr++;
if(ctr >= rotatingText.length) {
ctr = 1;
}
rotatingTextElement.innerHTML = rotatingText[ctr];
}
window.onload = initRotateText;

can i have some help?
thanks in advance