Ignore style definitions using a style ID that has already been used

3 files changed, 26 insertions, 1 deletions

diff --git a/NEWS b/NEWS
index 3025eea..f2ce8bb 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,7 @@
+# 1.11.0
+
+* Ignore style definitions using a style ID that has already been used.
+
 # 1.10.0
 
 * Add "Heading" and "Body" styles, as found in documents created by Apple Pages,
diff --git a/lib/docx/styles-reader.js b/lib/docx/styles-reader.js
index bff859f..28c809b 100644
--- a/lib/docx/styles-reader.js
+++ b/lib/docx/styles-reader.js
@@ -37,7 +37,18 @@ function readStylesXml(root) {
     root.getElementsByTagName("w:style").forEach(function(styleElement) {
         var style = readStyleElement(styleElement);
         var styleSet = styles[style.type];
-        if (styleSet) {
+
+        // Per 17.7.4.17 style (Style Definition) of ECMA-376 4th edition Part 1:
+        //
+        // > If multiple style definitions each declare the same value for their
+        // > styleId, then the first such instance shall keep its current
+        // > identifier with all other instances being reassigned in any manner
+        // > desired.
+        //
+        // For the purpose of conversion, there's no point holding onto styles
+        // with reassigned style IDs, so we ignore such style definitions.
+
+        if (styleSet && styleSet[style.styleId] === undefined) {
             styleSet[style.styleId] = style;
         }
     });
diff --git a/test/docx/styles-reader.tests.js b/test/docx/styles-reader.tests.js
index 0997d2c..b63bb6a 100644
--- a/test/docx/styles-reader.tests.js
+++ b/test/docx/styles-reader.tests.js
@@ -110,6 +110,16 @@ test('numbering style has numId read from paragraph properties', function() {
     assert.equal(styles.findNumberingStyleById("List1").numId, "42");
 });
 
+test('when multiple style elements have same style ID then only first element is used', function() {
+    var styles = readStylesXml(
+        new XmlElement("w:styles", {}, [
+            tableStyleElement("TableNormal", "Normal Table"),
+            tableStyleElement("TableNormal", "Table Normal")
+        ])
+    );
+    assert.equal(styles.findTableStyleById("TableNormal").name, "Normal Table");
+});
+
 function paragraphStyleElement(id, name) {
     return styleElement("paragraph", id, name);
 }