What Does (function() {})(); Syntax Work?

First question ever here. I'm a bit nervous to break the ice, please be indulgent I just finished the CodeAcademy JS lessons. In the following code that I found to toggle some of m

Solution 1:

fixed and absolute are position values not display

functiontoggledisplay(elementID) {
  var style = document.getElementById(elementID).style;
  style.position = style.position === 'fixed' ? 'absolute' : 'fixed';
};

body {
  position: relative;
}
#mydiv {
  top: 50px;
  left: 80px;
  min-height: 100px;
  width: 100px;
  background-color: lightgrey;
}

<buttononclick="toggledisplay('mydiv')">Toggle</button><divid="mydiv"></div>

Note: There is no real need to have the IIFE function, you can simply use a variable to refer to the style property