Question

I am looking for the proper method to embed javascript into an html parameter. This is an example of what I am trying to do:

  <img src="source.png" height="<script> if(screen.width == 1920)
                                {document.write('60px');}</script>" 
                                 title="icon"/>

I know embedding PHP in this manner can work, but I can not seem to get it to work with Javascript. My limited knowledge on the matter is to blame, and I need some help resolving this issue. Thanks.

Answer 1

Note the id="sourceImg" I added to the element, which must be unique per element per page. Not doing this will mean Javascript will not know which element to select, and will pick one.

<img id="sourceImg" src="source.png" title="icon">

<script>
if (screen.width == 1920) {
    document.getElementById('sourceImg').style.height = '60px';
}
</script>

That either needs to run after the markup falls in the source of the page, or in a window.onload event handler. If it runs before the img element is available, it will error out.

NOTE – JohnFx’s method that he describes in the comments below is:

<img id="sourceImg" src="source.png" title="icon" onload="sizeMe()">

<script>
function sizeMe() {
  if (screen.width == 1920) {
    document.getElementById('sourceImg').style.height = '60px';
  }
}
</script>

This uses the img element’s onload handler. Note that inline event handlers like onload="", onclick="", etc., are typically considered hard to maintain. The above should work, however, as a demonstration, and other routes involve understanding page loading, DOM element availability and other details which are potentially more difficult to understand than a simple example.

EDIT

And, technically, you could do this:

<img id="sourceImg"
     onload="if(screen.width < 1920) this.style.width='60px';"
     src="http://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/001_Jornal_Monsenhor_A_Comarca_23_de_Marco_de_1947.jpg/762px-001_Jornal_Monsenhor_A_Comarca_23_de_Marco_de_1947.jpg"
     title="icon">

http://jsfiddle.net/pdN3y/

Note, I changed the if statement to make the change more obvious.

But please don’t. It’s a bad idea and a bad habit to get into. Spend some time figuring out page loading and DOM availability, it’s time well spent.