fix: walk the group chain iteratively so deep nesting can't overflow the stack

rtf-group.js

@@ -9,18 +9,48 @@ class RTFGroup {
     this.style = {}
     this.ignorable = null
   }
+  // These walk up the group chain iteratively rather than by recursion. RTF
+  // groups nest via `{`, so the chain is as deep as the document nests it, and
+  // recursing once per lookup overflows the stack on deeply nested input. The
+  // walk stops at RTFDocument, which overrides each of these to return directly.
   get (name) {
-    return this[name] != null ? this[name] : this.parent.get(name)
+    for (let group = this; group != null; group = group.parent) {
+      if (group.parent == null) return group.get(name)
+      if (group[name] != null) return group[name]
+    }
   }
   getFont (num) {
-    return this.fonts[num] != null ? this.fonts[num] : this.parent.getFont(num)
+    for (let group = this; group != null; group = group.parent) {
+      if (group.parent == null) return group.getFont(num)
+      if (group.fonts[num] != null) return group.fonts[num]
+    }
   }
   getColor (num) {
-    return this.colors[num] != null ? this.colors[num] : this.parent.getFont(num)
+    for (let group = this; group != null; group = group.parent) {
+      if (group.parent == null) return group.getFont(num)
+      if (group.colors[num] != null) return group.colors[num]
+    }
   }
   getStyle (name) {
-    if (!name) return Object.assign({}, this.parent.getStyle(), this.style)
-    return this.style[name] != null ? this.style[name] : this.parent.getStyle(name)
+    if (!name) {
+      // Collect the chain, then merge root-first in a single pass. Recursing
+      // allocated a fresh object at every level for every lookup.
+      const chain = []
+      let group = this
+      while (group.parent != null) {
+        chain.push(group)
+        group = group.parent
+      }
+      const style = Object.assign({}, group.getStyle())
+      for (let i = chain.length - 1; i >= 0; i--) {
+        Object.assign(style, chain[i].style)
+      }
+      return style
+    }
+    for (let group = this; group != null; group = group.parent) {
+      if (group.parent == null) return group.getStyle(name)
+      if (group.style[name] != null) return group.style[name]
+    }
   }
   resetStyle () {
     this.style = {}