feat: prevent overwriting defined executors

Author: epoberezkin

README.md

@@ -106,6 +106,8 @@ Evaluate script. Returns Promise that resolves to the script evaluation result o
 
 Add executor to the interpreter. Can be an object or a function with methods.
 
+This method throws exception if you use the name that is already used (including predefined executors `array`, `calc` and `str`).
+
 
 ##### .addInstruction(Object definition, Function func)
 

lib/jsonscript.js

@@ -134,8 +134,7 @@ function addMacro(definition, _regenerateSchemas) {
  * @param {Object|Function} executor executor object or function
  */
 function addExecutor(name, executor) {
-  // TODO check duplicates, show warnings
-  // ? TODO whitelist methods?
+  if (this._executors[name]) throw new Error('executor "' + name + '" is already defined');
   this._executors[name] = executor;
 }
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "jsonscript-js",
-  "version": "0.5.0",
+  "version": "0.5.1",
   "description": "JavaScript interpreter for JSONScript",
   "main": "lib/jsonscript.js",
   "scripts": {

spec/jsonscript.spec.js

@@ -22,4 +22,13 @@ describe('jsonscript', function() {
       assert.strictEqual(js.validate.errors, null);
     });
   });
+
+
+  describe('method addExecutor', function() {
+    it('should throw if executor is already defined', function() {
+      assert.throws(function() {
+        js.addExecutor('calc', {});
+      });
+    });
+  });
 });