Onclick in a tag can't work with if statement

JavaScript
1

I don’t understand why the image swapping doesn’t work when I click the 2nd time:

<a href="JavaScript:;" onclick="if(document.getElementById('img-book_1').src!=='images/minimize.jpg'){document.getElementById('img-book_1').src='images/minimize.jpg';}else{document.getElementById('img-book_1').src='images/maximize.jpg';}"><img id="img-book_1" src="images/maximize.jpg" style="float: right;border: none;" /></a>

On the first click it swaps to the 2nd image but on the 2nd click it doesn’t swap back to the first.

2

src always contains the full URL regardless of what is assigned to it. Try:

<a href="#" onclick = "var img = document.getElementById('img-book_1'); img.src = ( img.src.search('minimize.jpg') > -1 ? 'images/maximize.jpg' : 'images/minimize.jpg' ); return false;">
 <img id="img-book_1" src="images/maximize.jpg" style="float: right;border: none;" />
</a>