Can't change background-image of a div
<p>I'm trying to change background-image of a div #image by hovering on thumbnail images (something like a simple slider)
My plunker is provided below.</p>

<p>1- First I tried to do like: element.style.backgroundImage
but i got this in the console: 
<a href="https://i.stack.imgur.com/lgbUH.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lgbUH.jpg" alt="Using .style.backgroundImage"></a></p>

<p>2- Then i tried something like element.backgroundImage
although it looks good in the console but didnt work, here is the console:
<a href="https://i.stack.imgur.com/AMdIJ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AMdIJ.jpg" alt="Without .style"></a></p>

<p>Note: I don't want to use any library, just want to study JavaScript core.</p>

<pre><code>      my plunker
</code></pre>

<p><a href="https://plnkr.co/edit/Mk0HSTYvQ4isVKjM7IEt?p=preview" rel="nofollow noreferrer">https://plnkr.co/edit/Mk0HSTYvQ4isVKjM7IEt?p=preview</a></p>

<h1>update:</h1>

<p>1- I noticed that i was doing wrong interpolation here:</p>

<pre><code>var bgI_value = 'url('+ src + ');';
</code></pre>

<p>it should be:</p>

<pre><code>var bgI_value = 'url("'+ src + '");';
</code></pre>

<p>2- The suggestion from Alexandru to remove the simicolon was a good point.</p>

<p>3- the suggestion from Sharma to add .style.backgroundImage was a good point too.</p>

<p>so my code was missing these three corrections!</p>

<p>Thanks all.</p>