javascript, querystring

<script>
if querystring("id") = "1" then
src="/Images/Design/Header.jpg"
elseif querystring("id") = "2" then
src="/Images/Design/Header2.jpg"
</script>

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I have below html codes on the webpage, and I want to apply above codes so it will dynamically loaded the images.
How can I do that in javascript?
<img alt="CaliforniaRentals" border="0" src="/Images/Design/Header.jpg" />

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CoolDev2014Asked:
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quizwedgeCommented:
First, you'll need to parse the querystring. There are a few ways to do that, but some are mentioned at http://www.joezimjs.com/javascript/3-ways-to-parse-a-query-string-in-a-url/ Not sure if you need help with that or if you've already got that.

Assuming that ID is the only querystring parameter (that is, your querystring is ?id=123) you can do something as simple as the following:

var id = window.location.search.substr(4);

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window.location.search contains the querystring and starts with a ?

Now that you have the id stored as id, the next step is to give your image an id.

Change that to

<img id="header_image" alt="CaliforniaRentals" border="0" src="/Images/Design/Header.jpg" />

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To actually change the image src you need the following code

if (id == "1") {
   document.getElementById("header_image").src="/Images/Design/Header.jpg";
} else if (id == "2") {
   document.getElementById("header_image").src="/Images/Design/Header2.jpg";
}

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That being said, if you're doing this on load, you'd be better off using whatever server side language you have access to so that the image doesn't load the default header and then change.
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Dave BaldwinFixer of ProblemsCommented:
That being said, if you're doing this on load, you'd be better off using whatever server side language you have access to so that the image doesn't load the default header and then change.
I definitely agree!
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