Better version of data-trim on code snippets

plugin/highlight/highlight.js

@@ -1,5 +1,52 @@
 // START CUSTOM REVEAL.JS INTEGRATION
 (function() {
+	// Function to perform a better "data-trim" on code snippets
+	// Will slice an indentation amount on each line of the snippet (amount based on the line having the lowest indentation length)
+	function betterTrim(snippetEl) {
+		// Helper functions
+		function trimLeft(val) {
+			// Adapted from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim#Polyfill
+			return val.replace(/^[\s\uFEFF\xA0]+/g, '');
+		}
+		function trimLineBreaks(input) {
+			var lines = input.split('\n');
+
+			// Trim line-breaks from the beginning
+			for (var i = 0; i < lines.length; i++) {
+				if (lines[i].trim() === '') {
+					lines.splice(i--, 1);
+				} else break;
+			}
+
+			// Trim line-breaks from the end
+			for (var i = lines.length-1; i >= 0; i--) {
+				if (lines[i].trim() === '') {
+					lines.splice(i, 1);
+				} else break;
+			}
+
+			return lines.join('\n');
+		}
+
+		// Main function for betterTrim()
+		return (function(snippetEl) {
+			var content = trimLineBreaks(snippetEl.innerHTML);
+			var lines = content.split('\n');
+			// Calculate the minimum amount to remove on each line start of the snippet (can be 0)
+			var pad = lines.reduce(function(acc, line) {
+				if (line.length > 0 && trimLeft(line).length > 0 && acc > line.length - trimLeft(line).length) {
+					return line.length - trimLeft(line).length;
+				}
+				return acc;
+			}, Number.POSITIVE_INFINITY);
+			// Slice each line with this amount
+			return lines.map(function(line, index) {
+				return line.slice(pad);
+			})
+			.join('\n');
+		})(snippetEl);
+	}
+
 	if( typeof window.addEventListener === 'function' ) {
 		var hljs_nodes = document.querySelectorAll( 'pre code' );
 
@@ -8,7 +55,7 @@
 
 			// trim whitespace if data-trim attribute is present
 			if( element.hasAttribute( 'data-trim' ) && typeof element.innerHTML.trim === 'function' ) {
-				element.innerHTML = element.innerHTML.trim();
+				element.innerHTML = betterTrim(element);
 			}
 
 			// Now escape html unless prevented by author