added position property to ParseError

src/ParseError.js

@@ -29,6 +29,8 @@ function ParseError(message, lexer, position) {
     var self = new Error(error);
     self.name = "ParseError";
     self.__proto__ = ParseError.prototype;
+
+    self.position = position;
     return self;
 }
 

test/katex-spec.js

@@ -1040,3 +1040,13 @@ describe("An accent builder", function() {
         expect(getBuilt("\\vec )^2")[0].classes).not.toContain("mclose");
     });
 });
+
+describe("A parser error", function () {
+    it("should report the position of an error", function () {
+        try {
+            parseTree("\\sqrt}");
+        } catch (e) {
+            expect(e.position).toEqual(5);
+        }
+    });
+});