Spread and Rest Operators in JavaScript
The spread and rest operators, both represented by three dots (...), are versatile features in JavaScript introduced in ES6. Although they share the same syntax, they serve distinct purposes: the spread operator is used for expanding elements, while the rest operator is used for collecting elements.
1. Spread Operator
The spread operator is used to expand elements of an array, object, or iterable into individual elements.
A. Spreading in Arrays
The spread operator can be used to copy, concatenate, or pass array elements.
Example: Copying Arrays
const arr1 = [1, 2, 3]; const arr2 = [...arr1]; // Creates a copy of arr1 console.log(arr2); // Output: [1, 2, 3]
Example: Concatenating Arrays
const arr1 = [1, 2, 3]; const arr2 = [4, 5, 6]; const combined = [...arr1, ...arr2]; console.log(combined); // Output: [1, 2, 3, 4, 5, 6]
Example: Passing Elements to Functions
const numbers = [10, 20, 30]; console.log(Math.max(...numbers)); // Output: 30
B. Spreading in Objects
You can use the spread operator to copy or merge objects.
Example: Copying Objects
const obj1 = { a: 1, b: 2 };
const obj2 = { ...obj1 };
console.log(obj2); // Output: { a: 1, b: 2 }
Example: Merging Objects
const obj1 = { a: 1, b: 2 };
const obj2 = { b: 3, c: 4 };
const merged = { ...obj1, ...obj2 };
console.log(merged); // Output: { a: 1, b: 3, c: 4 }
2. Rest Operator
The rest operator collects multiple elements into a single array or object. It is commonly used in function parameters or destructuring assignments.
A. Using Rest in Function Parameters
The rest operator can collect an indefinite number of arguments into an array.
Example: Collecting Arguments
function sum(...numbers) {
return numbers.reduce((total, num) => total + num, 0);
}
console.log(sum(1, 2, 3, 4)); // Output: 10
B. Using Rest in Destructuring Arrays
The rest operator collects remaining elements in an array destructuring operation.
Example: Array Destructuring
const [first, second, ...rest] = [1, 2, 3, 4, 5]; console.log(first); // Output: 1 console.log(second); // Output: 2 console.log(rest); // Output: [3, 4, 5]
C. Using Rest in Destructuring Objects
The rest operator collects remaining properties in an object destructuring operation.
Example: Object Destructuring
const arr1 = [1, 2, 3]; const arr2 = [...arr1]; // Creates a copy of arr1 console.log(arr2); // Output: [1, 2, 3]
3. Key Differences Between Spread and Rest Operators
|
Spread Operator |
Rest Operator | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Purpose | Expands elements into individual items | Collects items into a single entity | ||||||||||||
| Use Cases | Copying, merging, passing elements | Collecting function arguments, destructuring | ||||||||||||
Data Typesconst arr1 = [1, 2, 3]; const arr2 = [4, 5, 6]; const combined = [...arr1, ...arr2]; console.log(combined); // Output: [1, 2, 3, 4, 5, 6] |
Arrays, Objects, Iterables | Arrays, Objects |
4. Practical Examples
const numbers = [10, 20, 30]; console.log(Math.max(...numbers)); // Output: 30
A. Swapping Array Elements
- B. Combining Rest with Spread
- 5. Summary
Spread Operator (...): Expands arrays, objects, or iterables into individual elements.
The above is the detailed content of Mastering Spread and Rest Operators in JavaScript. For more information, please follow other related articles on the PHP Chinese website!
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