javaScript will not let me write to a textbox value

Question

EDIT thanks to everyone!

I have a cookie on a page and when the page loads I want to put the value from the cookie into a input box as its defualt value.

However it will not work and I cant find the problem. I even made a test div and tried to change that but it wont work.

function checkCookie() {
    var cookieName = getCookie("username");

    if (cookieName != null && cookieName != "") {
        alert(cookieName);
        document.getElementById("fname").value = cookieName
    } else {
        alert("else");
        return;
    }
}

Here is the html

<input type="text" name="fname" id="fname" onKeyUp="isName(this.value)">

I tried this code as well (I just made a div called tester2

document.getElementById("fname").value = "hello" 

doesnt work

document.getElementById("tester2").innerHTML = cookieName

doesnt work

Nothing works. It will not let me change a element within this function. If I try and put the code (ie document.etcetc.innerHTML = "hi") in another function then it works perfectly... however it will not run as shown above. Its driving me crazy.

Any ideas?

Answer 1

I suspect that when the checkCookie function executes, the DOM is not ready yet and your input doesn't exist.

To make sure it's not the case, try the following:

 window.onload = checkCookie;

This will execute the checkCookie function only when the window content has been loaded. It is not the most efficient way to do it, but since I don't know which browser you are using, it was the most reliable way to test.

EDIT: After taking a look at your code, the problem is this line:

window.onload = checkCookie();

That will execute the checkCookie function right away and try to assign the function's result to window.onload.

Check in my previous example to see how it should be done.