spred and rest operator

Author: nilajcoder

Programs/rest.js

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+
+
+/*
+
+
+The rest operator in JavaScript (also written as ...) is used to
+ collect multiple elements into a single array or object. It’s the opposite of the spread operator.
+
+🔹 Use of ... as Rest Operator
+It is used to:
+
+Collect function arguments
+
+Gather remaining array or object elements during destructuring
+
+✅ 1. Rest in Function Parameters
+Collects all remaining arguments into an array.
+
+javascript
+Copy
+Edit
+function sum(...numbers) {
+  return numbers.reduce((total, num) => total + num, 0);
+}
+
+console.log(sum(1, 2, 3)); // 6
+console.log(sum(5, 10, 15, 20)); // 50
+✅ 2. Rest in Array Destructuring
+javascript
+Copy
+Edit
+const [first, second, ...others] = [1, 2, 3, 4, 5];
+
+console.log(first);  // 1
+console.log(second); // 2
+console.log(others); // [3, 4, 5]
+✅ 3. Rest in Object Destructuring
+javascript
+Copy
+Edit
+const person = {
+  name: "Ram",
+  age: 25,
+  city: "Delhi",
+  country: "India"
+};
+
+const { name, ...rest } = person;
+
+console.log(name); // "Ram"
+console.log(rest); // { age: 25, city: "Delhi", country: "India" }
+⚠️ Rest vs Spread
+Feature	Rest Operator	Spread Operator
+Collects values	Yes	No
+Expands values	No	Yes
+Syntax	...	...
+Use case	Function args, destructuring	Function calls, cloning, merging
+*/

Programs/spreadop.js

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+
+
+/*
+
+The spread operator (...) in JavaScript is used to expand elements
+ of an array or object into individual elements. It’s very useful for copying, merging, and passing data.
+
+🔹 Syntax:
+javascript
+Copy
+Edit
+...iterable
+It works with arrays, objects, and function arguments.
+
+✅ 1. Spread in Arrays
+👉 Copying an Array
+javascript
+Copy
+Edit
+const arr1 = [1, 2, 3];
+const arr2 = [...arr1];
+
+console.log(arr2); // [1, 2, 3]
+👉 Merging Arrays
+javascript
+Copy
+Edit
+const a = [1, 2];
+const b = [3, 4];
+const merged = [...a, ...b];
+
+console.log(merged); // [1, 2, 3, 4]
+✅ 2. Spread in Objects
+👉 Copying an Object
+javascript
+Copy
+Edit
+const obj1 = { x: 1, y: 2 };
+const obj2 = { ...obj1 };
+
+console.log(obj2); // { x: 1, y: 2 }
+👉 Merging Objects
+javascript
+Copy
+Edit
+const objA = { a: 1 };
+const objB = { b: 2 };
+const merged = { ...objA, ...objB };
+
+console.log(merged); // { a: 1, b: 2 }
+✅ 3. Spread in Function Calls
+javascript
+Copy
+Edit
+const nums = [1, 2, 3];
+
+function add(x, y, z) {
+  return x + y + z;
+}
+
+console.log(add(...nums)); // 6
+⚠️ Note: Spread vs Rest
+... is spread when expanding values.
+
+... is rest when collecting values.
+
+Spread (expanding)
+javascript
+Copy
+Edit
+const arr = [1, 2, 3];
+console.log(...arr); // 1 2 3
+Rest (collecting)
+javascript
+Copy
+Edit
+function sum(...numbers) {
+  return numbers.reduce((a, b) => a + b, 0);
+}
+
+sum(1, 2, 3); // 6
+*/