Fix: better math rendering for mchoice

Author: bnmnetp

runestone/mchoice/js/mchoice.js

@@ -49,9 +49,13 @@ export default class MultipleChoice extends RunestoneBase {
         this.createMCForm();
         this.addCaption("runestone");
         this.checkServer("mChoice", true);
-        $(document).on("runestone:mathjax-ready", function () {
-            this.queueMathJax(this.containerDiv);
-        });
+        let self = this;
+        // https://docs.mathjax.org/en/latest/options/startup/startup.html
+        // https://docs.mathjax.org/en/latest/web/configuration.html#startup-action
+        // runestoneMathReady is defined in the preamble for all PTX authored books
+        if (typeof runestoneMathready !== "undefined") {
+            runestoneMathReady.then(() => self.queueMathJax(self.containerDiv));
+        }
     }
 
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