Core: IE11 workaround for currentScript (#2104)

This adds a new function `Prism.util.currentScript` which is a functionally equalent to `document.currentScript` but includes support for IE11.

components/prism-core.js

@@ -101,6 +101,48 @@ var _ = {
 				default:
 					return o;
 			}
+		},
+
+		/**
+		 * Returns the script element that is currently executing.
+		 *
+		 * This does __not__ work for line script element.
+		 *
+		 * @returns {HTMLScriptElement | null}
+		 */
+		currentScript: function () {
+			if (typeof document === 'undefined') {
+				return null;
+			}
+			if ('currentScript' in document) {
+				return document.currentScript;
+			}
+
+			// IE11 workaround
+			// we'll get the src of the current script by parsing IE11's error stack trace
+			// this will not work for inline scripts
+
+			try {
+				throw new Error();
+			} catch (err) {
+				// Get file src url from stack. Specifically works with the format of stack traces in IE.
+				// A stack will look like this:
+				//
+				// Error
+				//    at _.util.currentScript (http://localhost/components/prism-core.js:119:5)
+				//    at Global code (http://localhost/components/prism-core.js:606:1)
+
+				var src = (/at [^(\r\n]*\((.*):.+:.+\)$/i.exec(err.stack) || [])[1];
+				if (src) {
+					var scripts = document.getElementsByTagName('script');
+					for (var i in scripts) {
+						if (scripts[i].src == src) {
+							return scripts[i];
+						}
+					}
+				}
+				return null;
+			}
 		}
 	},
 
@@ -527,7 +569,7 @@ if (!_self.document) {
 }
 
 //Get current script and highlight
-var script = document.currentScript || [].slice.call(document.getElementsByTagName('script')).pop();
+var script = _.util.currentScript();
 
 if (script) {
 	_.filename = script.src;

plugins/autoloader/prism-autoloader.js

@@ -181,25 +181,24 @@
 	var lang_data = {};
 
 	var ignored_language = 'none';
-
-	var scripts = document.getElementsByTagName('script');
-	var script = scripts[scripts.length - 1];
 	var languages_path = 'components/';
 
-	var autoloaderFile = /\bplugins\/autoloader\/prism-autoloader\.(?:min\.)js$/i;
-	var prismFile = /[\w-]+\.(?:min\.)js$/i;
-
-	if (script.hasAttribute('data-autoloader-path')) {
-		// data-autoloader-path is set, so just use it
-		languages_path = script.getAttribute('data-autoloader-path').trim().replace(/\/?$/, '/');
-	} else {
-		var src = script.src;
-		if (autoloaderFile.test(src)) {
-			// the script is the original autoloader script in the usual Prism project structure
-			languages_path = src.replace(autoloaderFile, 'components/');
-		} else if (prismFile.test(src)) {
-			// the script is part of a bundle like a custom prism.js from the download page
-			languages_path = src.replace(prismFile, 'components/');
+	var script = Prism.util.currentScript();
+	if (script) {
+		var autoloaderFile = /\bplugins\/autoloader\/prism-autoloader\.(?:min\.)js$/i;
+		var prismFile = /[\w-]+\.(?:min\.)js$/i;
+		if (script.hasAttribute('data-autoloader-path')) {
+			// data-autoloader-path is set, so just use it
+			languages_path = script.getAttribute('data-autoloader-path').trim().replace(/\/?$/, '/');
+		} else {
+			var src = script.src;
+			if (autoloaderFile.test(src)) {
+				// the script is the original autoloader script in the usual Prism project structure
+				languages_path = src.replace(autoloaderFile, 'components/');
+			} else if (prismFile.test(src)) {
+				// the script is part of a bundle like a custom prism.js from the download page
+				languages_path = src.replace(prismFile, 'components/');
+			}
 		}
 	}