rest operator

davemOps · davemOps · commit c96dd9a456aa · 2025-10-17T17:13:18.000+03:00
diff --git a/ES6-features/restOperator.js b/ES6-features/restOperator.js
@@ -0,0 +1,79 @@
+
+// ES6 Rest Operator (...)
+
+// The rest operator collects multiple elements into a single array or object.
+// It looks exactly like the spread operator (...), but it works in the opposite direction.
+// Spread &rarr; expands items
+// Rest   &rarr; collects items
+
+
+//  Rest with Arrays (Function Arguments)
+
+// The rest parameter allows a function to accept any number of arguments as an array.
+
+function sum(...numbers) {
+  return numbers.reduce((total, n) => total + n, 0);
+}
+
+console.log(sum(1, 2, 3));       // Output: 6
+console.log(sum(5, 10, 15, 20)); // Output: 50
+
+//  Rest in Array Destructuring
+
+const fruits = ["apple", "banana", "mango", "orange", "grape"];
+
+const [first, second, ...others] = fruits;
+console.log(first);  // Output: apple
+console.log(second); // Output: banana
+console.log(others); // Output: ['mango', 'orange', 'grape']
+
+
+//  Rest with Objects
+
+const user = {
+  name: "David",
+  age: 80,
+  country: "Kenya",
+  profession: "Developer"
+};
+
+const { name, ...details } = user;
+console.log(name);    // Output: David
+console.log(details); // Output: { age: 80, country: 'Kenya', profession: 'Developer' }
+
+// Combining Spread & Rest
+
+// Spread expands &rarr; Rest collects
+
+const numbers = [10, 20, 30, 40, 50];
+
+// Spread: Pass array elements individually
+const newNumbers = [...numbers, 60, 70];
+console.log(newNumbers); // Output: [10, 20, 30, 40, 50, 60, 70]
+
+// Rest: Collect multiple elements into one variable
+const [firstNum, ...remaining] = newNumbers;
+console.log(firstNum);   // Output: 10
+console.log(remaining);  // Output: [20, 30, 40, 50, 60, 70]
+
+
+//  Real-life Example
+
+function introduce(firstName, lastName, ...hobbies) {
+  console.log(`Name: ${firstName} ${lastName}`);
+  console.log(`Hobbies: ${hobbies.join(", ")}`);
+}
+
+introduce("Macharia", "David", "Coding", "Reading", "Cycling");
+// Output:
+// Name: Macharia David
+// Hobbies: Coding, Reading, Cycling
+
+// Summary
+
+// - Rest Operator collects multiple values into one array or object.
+// - Common uses: function parameters & destructuring.
+// - Syntax: (...variableName)
+// - Difference:
+//   &rarr; Spread expands (breaks apart arrays/objects)
+//   &rarr; Rest collects (gathers items into one variable)
