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

1 files changed, 12 insertions, 1 deletions

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;
         }
     });