I'm trying to learn Javascript and here is an issue I can't resolve.. I have this html tag 

```
  <img id="img1" src="" class="img-thumbnail" style="display:none;" />
  <input id="addimg" type="button" value="Save URL" onclick='SaveUrl()'/>

```

and with Javascript I want to check if image source is empty here are a Javascript functions:

```
function SaveUrl() {
    var url = document.getElementById("ImageUrl").value;
    SaveImgUrl(url);
    ClearUrl();
}

function SaveImgUrl(url) {
        var img = document.getElementById("img1");
        if (img.src.length == 0) {
            img.src = url;
            img.style = "block";
        }

```

Problem is with if statement I mean it returns false when source value is "" I also tried if(img.src == "") but that doesn't help as well. also I know there are simplier solutions provided by jQuery but I want to solve it with simple Javascript without using any frameworks.. please help :)