Add dereferenceUses plugin

plugins/dereferenceUses.js

@@ -0,0 +1,116 @@
+'use strict';
+
+const { querySelectorAll, querySelector } = require('../lib/xast.js');
+
+exports.type = 'full';
+
+exports.active = true;
+
+exports.description = 'dereferences <use/> elements';
+
+exports.params = {
+  keepHref: false, // keep (xlink:)href attributes
+
+  symbolContainer: 'svg', // browsers use <svg/> as container of <symbol/> content (`g` could also be used)
+};
+
+const OverridingUseAttributeNames = [
+  'x',
+  'y',
+  'width',
+  'height',
+  'href',
+  'xlink:href',
+];
+const HrefAttributeNames = ['href', 'xlink:href'];
+
+/**
+ * Dereferences <use> elements
+ *
+ *
+ * @param {Object} document document element
+ * @param {Object} options plugin params
+ *
+ * @author strarsis <[email protected]>
+ */
+exports.fn = function (document, options) {
+  options = options || {};
+
+  // collect <use/>s
+  const useElements = querySelectorAll(document, 'use');
+
+  // no <use/>s, nothing to do
+  if (useElements === null) {
+    return document;
+  }
+
+  // replace each <use/> with its referenced node
+  for (const useElement of useElements) {
+    // `href`/`xlink:href` value
+    const hrefAttribute = useElement.attr('href')
+      ? useElement.attr('href')
+      : useElement.attr('xlink:href');
+    if (!hrefAttribute || hrefAttribute.value.length === 0) continue;
+    const href = hrefAttribute.value;
+
+    // look up referenced element
+    const targetElement = querySelector(document, href);
+    if (!targetElement) continue;
+
+    // clone referenced element for insertion
+    const insertElement = targetElement.clone();
+
+    // Attribute inheritance of the referenced element
+    // @see https://developer.mozilla.org/en-US/docs/Web/SVG/Element/use
+    //   "Only the attributes x, y, width, height and href on the use element will override those set on the referenced element.
+    //    However, any other attributes not set on the referenced element will be applied to the use element."
+    const insertElementAttributeNames = Object.keys(insertElement.attributes);
+    for (const attributeName in useElement.attributes) {
+      // don't remove attributes from the referenced element that, by specs, override the one of the <use> element
+      if (
+        insertElementAttributeNames.includes(attributeName) &&
+        !OverridingUseAttributeNames.includes(attributeName)
+      )
+        continue;
+
+      // don't remove href attribute with keepHref option turned on
+      if (!options.keepHref && HrefAttributeNames.includes(attributeName))
+        continue;
+
+      // set overriding attributes from referenced node
+      insertElement.attributes[attributeName] =
+        useElement.attributes[attributeName];
+    }
+
+    // only the original node is allowed to have this ID (IDs must be unique)
+    delete insertElement.attributes['id'];
+
+    // <symbol/> elements are template elements (hence not visible),
+    // browsers would place a <symbol/> element as a different element
+    if (insertElement.isElem('symbol')) {
+      insertElement.name = options.symbolContainer;
+    }
+
+    // apply styles of <use/> element on top of the referenced Element
+    const useElementProperties = useElement.style.getProperties();
+    for (const propertyName in useElementProperties) {
+      const property = useElementProperties[propertyName];
+
+      insertElement.style.setProperty(
+        propertyName,
+        property.value,
+        property.priority
+      );
+    }
+
+    // replace the <use/> element with the referenced element
+    const useParentElement = useElement.parentNode;
+
+    // position of <use/> in parent
+    const useElementPosition = useParentElement.children.indexOf(useElement);
+
+    useParentElement.children.splice(useElementPosition, 1, insertElement);
+  }
+
+  return document;
+};

plugins/plugins.js

@@ -34,6 +34,7 @@ exports.removeEmptyContainers = require('./removeEmptyContainers.js');
 exports.removeEmptyText = require('./removeEmptyText.js');
 exports.removeHiddenElems = require('./removeHiddenElems.js');
 exports.removeMetadata = require('./removeMetadata.js');
+exports.dereferenceUses = require('./dereferenceUses.js');
 exports.removeNonInheritableGroupAttrs = require('./removeNonInheritableGroupAttrs.js');
 exports.removeOffCanvasPaths = require('./removeOffCanvasPaths.js');
 exports.removeRasterImages = require('./removeRasterImages.js');