Add better error messages for errors parsing and evaluating JS code (#1727)

* Add better error messages for errors parsing and evaluating JS code

* Grunt

NEWS.md

@@ -11,6 +11,8 @@ shiny 1.0.3.9000
 
 Addressed [#1501](https://github.com/rstudio/shiny/issues/1501): The `fileInput` control now retains uploaded file extensions on the server. This fixes [readxl](https://github.com/tidyverse/readxl)'s `readxl::read_excel` and other functions that must recognize a file's extension in order to work. ([#1706](https://github.com/rstudio/shiny/pull/1706))
 
+For `conditionalPanel`s, Shiny now gives more informative messages if there are errors evaluating or parsing the JavaScript conditional expression. ([#1727](https://github.com/rstudio/shiny/pull/1727))
+
 ### Bug fixes
 
 Fixed [#1701](https://github.com/rstudio/shiny/issues/1701): There was a partial argument match in the `generateOptions` function. ([#1702](https://github.com/rstudio/shiny/pull/1702))

inst/www/shared/shiny.js

@@ -175,7 +175,14 @@ var _typeof = typeof Symbol === "function" && typeof Symbol.iterator === "symbol
   // "with" on the argument value, and return the result.
   function scopeExprToFunc(expr) {
     /*jshint evil: true */
-    var func = new Function("with (this) {return (" + expr + ");}");
+    var expr_escaped = expr.replace(/[\\"']/g, '\\$&').replace(/\u0000/g, '\\0');
+    try {
+      var func = new Function('with (this) {\n        try {\n          return (' + expr + ');\n        } catch (e) {\n          console.error(\'Error evaluating expression: ' + expr_escaped + '\');\n          throw e;\n        }\n      }');
+    } catch (e) {
+      console.error("Error parsing expression: " + expr);
+      throw e;
+    }
+
     return function (scope) {
       return func.call(scope);
     };

srcjs/utils.js

@@ -161,7 +161,24 @@ function pixelRatio() {
 // "with" on the argument value, and return the result.
 function scopeExprToFunc(expr) {
   /*jshint evil: true */
-  var func = new Function("with (this) {return (" + expr + ");}");
+  var expr_escaped = expr.replace(/[\\"']/g, '\\$&').replace(/\u0000/g, '\\0');
+  try {
+    var func = new Function(
+      `with (this) {
+        try {
+          return (${expr});
+        } catch (e) {
+          console.error('Error evaluating expression: ${expr_escaped}');
+          throw e;
+        }
+      }`
+    );
+  } catch (e) {
+    console.error("Error parsing expression: " + expr);
+    throw e;
+  }
+
+
   return function(scope) {
     return func.call(scope);
   };