lab15: impl

lab15/smart-array.js

@@ -18,24 +18,24 @@ function SmartArray(...args) {
         let end = parseInt(prop.replace(RANGE_PAT, "$2")) + 1;
         return target.slice(start, end);
       } else if (prop.match(FROM_END_PAT)) {
-        //
-        // ***YOUR CODE HERE***
-        //
         // Return the element at the specified position, counting
         // back from target.length.  So "-1" will refer to the last
         // element in the array.
         //
         // If the resulting index position is negative,
         // raise an exception.
+        let indexFromEnd = parseInt(prop.replace(FROM_END_PAT, "$1"));
+        let index = target.length - indexFromEnd;
+        if (index < 0) {
+          throw new Error("Index out of bounds");
+        }
+        return Reflect.get(target, index);
       } else {
         // Do the usual array thing -- get the value at the specified index.
         return Reflect.get(...arguments);
       }
     },
     set: function(target, prop, newVal) {
-      //
-      // ***YOUR CODE HERE***
-      //
       // For smart arrays, we only allow updates to numerical fields.
       // Throw an exception for a 'prop' that is not a valid integer.
       //
@@ -43,7 +43,33 @@ function SmartArray(...args) {
       //
       // If negative, update the position counting from the end of the array.
       // However, raise an exception if the resulting index is still negative.
+      if (!prop.match(NUM_PAT)) {
+        throw new Error("Invalid index for assignment");
+      }
+      let index = parseInt(prop);
+      if (index < 0) {
+        index = target.length + index;
+        if (index < 0) {
+          throw new Error("Index out of bounds");
+        }
+      }
+      Reflect.set(target, index, newVal);
+      return true;
     },
+    deleteProperty: function(target, prop) {
+      if (!prop.match(NUM_PAT)) {
+        throw new Error("Invalid index for deletion");
+      }
+      let index = parseInt(prop);
+      if (index < 0) {
+        index = target.length + index;
+        if (index < 0) {
+          throw new Error("Index out of bounds");
+        }
+      }
+      target.splice(index, 1);
+      return true;
+    }
   });
 }
 
@@ -78,9 +104,10 @@ try {
 }
 
 try {
-  arr[3*"hello"] = 'hello';
+  arr[3 * "hello"] = 'hello';
 } catch (e) {
   console.log("Exception correctly thrown.");
 }
 
+delete arr[-2];
 console.log(arr);