update handler

Author: MetaMmodern

src/expander/handler.js

@@ -1,13 +1,18 @@
+/* eslint-disable no-eval */
 const Stack = require("./stack");
 
 const argsStack = new Stack();
 const operators = ["+", "-", "*", "/", "%"];
 
 function handle(arg) {
   if (operators.includes(arg)) {
+    if (argsStack.Length < 2) {
+      throw new Error(
+        `Can't calculate: ${argsStack.Length} elements are in stack. Check your syntax.`
+      );
+    }
     const first = argsStack.pop();
     const second = argsStack.pop();
-    // eslint-disable-next-line no-eval
     const result = eval(`${second} ${arg} ${first}`);
     argsStack.push(result);
   }