Fix invert implementation and add tests

Author: Richiealx

Sprint-2/interpret/invert.js

@@ -4,26 +4,79 @@
 // When invert is passed this object
 // Then it should swap the keys and values in the object
 
-// E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
+// Example:
+// invert({ x: 10, y: 20 })
+// should return:
+// { "10": "x", "20": "y" }
 
-function invert(obj) {
-  const invertedObj = {};
+/*
+a) What is the current return value when invert({ a: 1 }) is called?
 
-  for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
-  }
+Current output:
+{ key: 1 }
 
-  return invertedObj;
+Reason:
+The code uses invertedObj.key which creates a property literally called "key"
+instead of using the variable key.
+
+---------------------------------------------------
+
+b) What is the current return value when invert({ a: 1, b: 2 }) is called?
+
+Current output:
+{ key: 2 }
+
+Reason:
+The second iteration overwrites the first value because the property name
+is always "key".
+
+---------------------------------------------------
+
+c) What is the target return value when invert({ a: 1, b: 2 }) is called?
+
+Expected output:
+{
+  "1": "a",
+  "2": "b"
 }
 
-// a) What is the current return value when invert is called with { a : 1 }
+Keys and values should be swapped.
+
+---------------------------------------------------
 
-// b) What is the current return value when invert is called with { a: 1, b: 2 }
+d) What does Object.entries return? Why is it needed?
 
-// c) What is the target return value when invert is called with {a : 1, b: 2}
+Object.entries(obj) converts an object into an array of [key, value] pairs.
 
-// c) What does Object.entries return? Why is it needed in this program?
+Example:
+Object.entries({ a: 1, b: 2 })
 
-// d) Explain why the current return value is different from the target output
+returns:
+[
+  ["a", 1],
+  ["b", 2]
+]
+
+This allows us to loop through object properties using for...of.
+
+---------------------------------------------------
+
+e) Why is the current return value different from the target output?
+
+Because invertedObj.key uses the literal property name "key".
+To use the value dynamically as the key, we must use bracket notation:
+invertedObj[value] = key;
+*/
+
+function invert(obj) {
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    // Correct implementation: swap key and value
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
 
-// e) Fix the implementation of invert (and write tests to prove it's fixed!)
+module.exports = invert;

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,20 @@
+const invert = require("./invert.js");
+
+describe("invert()", () => {
+  test("inverts a single key-value pair", () => {
+    expect(invert({ a: 1 })).toEqual({
+      1: "a",
+    });
+  });
+
+  test("inverts multiple key-value pairs", () => {
+    expect(invert({ a: 1, b: 2 })).toEqual({
+      1: "a",
+      2: "b",
+    });
+  });
+
+  test("returns an empty object for empty input", () => {
+    expect(invert({})).toEqual({});
+  });
+});