Check For Internet Explorer (IE) Compatibility Mode

Create a JavaScript file called iecheck.js and paste the following in the snippet:

function trueOrFalse() {
 return true;
}

function IeVersion() {
 // Set defaults
 var value = {
 IsIE: false,
 TrueVersion: 0,
 ActingVersion: 0,
 CompatibilityMode: false
 };

// Try to find the Trident version number
 var trident = navigator.userAgent.match(/Trident\/(\d+)/);
 if (trident) {
 value.IsIE = true;
 //Convert from the Trident version number to the IE version number
 value.TrueVersion = parseInt(trident[1], 10) + 4;
 }

// Try to find the MSIE number
 var msie = navigator.userAgent.match(/MSIE (\d+)/);
 if (msie) {
 value.IsIE = true;
 // Find the IE version number from the user agent string
 value.ActingVersion = parseInt(msie[1]);
 } else {
 // Must be IE 11 in "edge" mode
 value.ActingVersion = value.TrueVersion;
 }

// If we have both a Trident and MSIE version number, see if they're different
 if (value.IsIE && value.TrueVersion > 0 && value.ActingVersion > 0) {
 // In compatibility mode if the trident number doesn't match up with the MSIE number
 value.CompatibilityMode = value.TrueVersion != value.ActingVersion;
 }
 return value;
}

Once you have the JavaScript file then open your page where you are going to check for compatibility for and place a reference to the iecheck.js file in the head tag.

<script src="iecheck.js" type="text/javascript"></script>

After that you have multiple options on how to use the script.

For example, if you would like to check for compatibility and redirect then paste the following snippet inside of the body of your html:

<script type="text/javascript">
// 0 = not in compatibility view, 1 = in compatibility view
var ie = IeVersion();
if ((ie.CompatibilityMode == "0") && (ie.IsIE == "1")) {
window.location = "redirecttosomewhere.html"
}
else {
// do nothing, is in compatibility view
}
</script>

Another example would be if you just want to see the results on the page; just place this snippet inside of the body of your html:

<script type="text/javascript">
// <![CDATA[
var ie = IeVersion();
document.write("IsIE: " + ie.IsIE + "</br>");
document.write("TrueVersion: " + ie.TrueVersion + "</br>");
document.write("ActingVersion: " + ie.ActingVersion + "</br>");
document.write("CompatibilityMode: " + ie.CompatibilityMode + "</br>");
// ]]>
</script>

Hope this helps. Questions are always welcome.