In a situation where the x-ua-compatible meta tag is being used, such as the simple example below...
<html>
<head>
<title>A Test Site</title>
<meta http-equiv="x-ua-compatible" content="IE=EmulateIE8">
<script>
function displayMessage(msg) {
alert(msg);
}
</script>
</head>
<body onLoad="displayMessage('Hello World!');">
</body>
</html>
...does this affect the Javascript performance of Internet Explorer? As I understand it, the tag affects which of the rendering engines are used to display a page (MSDN reference).
Does using the tag change how Javascript is executed on a page or is this divorced from the rendering engine (so I could display a page to Internet Explorer 8 standards but run the Javascript with the JavaScript engine used in Internet Explorer 11 for example)?
The
x-ua-compatibledirective does change your JavaScript. There are some things that still exist when you're in a legacy document mode, but by and large, you'll get a JavaScript environment and syntax that looks and feels like it did during the days of the legacy environment.I work on the Microsoft Edge team, and am happy to address any specific issues you may have with JavaScript, legacy document modes, and supporting older instances of Internet Explorer.