if statement display none javascript correspond to library tags {{IMAGE}}

<div id="title1"><img src="a.jpg"></div>
<div id="title2"><img src="b.jpg"></div>
<div id="title3"><img src="c.jpg"></div>



<script type="text/javasctipt">
if ("{{IMAGE(z1)}}" = "") { document.getElementById('title1').style.display = "none"; }
if ("{{IMAGE(z2)}}" = "") { document.getElementById('title2').style.display = "none"; }
if ("{{IMAGE(z3)}}" = "") { document.getElementById('title3').style.display = "none"; }  
</script>

I like to have these div tags title1, title2, title3 disappear when {{IMAGE(z1}}, {{IMAGE(z2}} and {{IMAGE(z3}} are not exist. These tags are the library tags for image uploads. In other words, When the image is not uploaded, these div tags will be display: none

But my javascript is not working, any idea why? Thanks in advance. Oh and Please I need this to be done in only Javascript, nojQuery please.