How to use javascript variable in iframe src

how to write javascript variable in iframe src?

<iframe id="showskill" scrolling="yes" height="350" width ="350" src="http://localhost/POSkill/skillshow.aspx?user_id="+ ReturnURL() ></iframe>

Here ReturnURL() is a javascript function which returns a value. But the problem is in the iframe source I'm not getting the returned value of the function. Am I not putting in the right format or missing something?

Thanks in advance Johnny

Solution

You can't use JavaScript variables or functions directly within your html markup in that manner. What you can do is define your iframe first and then set its source from JavaScript:

<iframe id="showskill" scrolling="yes" height="350" width ="350" src=""></iframe>

<script>
    document.getElementById("showskill").src =
              "http://localhost/POSkill/skillshow.aspx?user_id="+ ReturnURL();
</script>

There are several other ways to achieve something similar, but I don't really want to go through them all when I'm not sure quite what your context is.