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src/util/MergeDefault.js

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+'use strict';
+
+module.exports = function merge(def, given) {
+	if (!given) {
+		return def;
+	}
+
+	given = given || {};
+
+	for (var key in def) {
+		if (!given.hasOwnProperty(key)) {
+			given[key] = def[key];
+		} else if (given[key] === Object(given[key])) {
+			given[key] = merge(def[key], given[key]);
+		}
+	}
+
+	return given;
+};