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Ques: What is an Array in JavaScript?
Ans: An Array in JavaScript is a special type of object used to store multiple values in a single variable. Each value is stored at a numeric index, starting from 0.
Example:
let fruits = ["Apple", "Banana", "Cherry"];
console.log(fruits[0]); // Apple
Ques: How do you create an Array in JavaScript?
Ans: There are two ways to create arrays:
Array Literal (Recommended):
let colors = ["Red", "Green", "Blue"];
Array Constructor:
let numbers = new Array(1, 2, 3, 4);
Ques: What are Array Indexes in JavaScript?
Ans: Each element in an array has an index that starts at 0. You can access, modify, or delete elements using these indexes.
Example:
let cars = ["BMW", "Audi", "Tesla"];
cars[1] = "Mercedes"; // modifies element
console.log(cars[1]); // Mercedes
Ques: How can you find the length of an array?
Ans: Use the .length property.
Example:
let cities = ["Delhi", "London", "Paris"];
console.log(cities.length); // 3
Ques: What are common Array methods in JavaScript?
| Method | Description | Example |
|---|---|---|
push() |
Adds element to end | arr.push("x") |
pop() |
Removes last element | arr.pop() |
unshift() |
Adds element to start | arr.unshift("x") |
shift() |
Removes first element | arr.shift() |
concat() |
Merges arrays | arr1.concat(arr2) |
join() |
Converts to string | arr.join(",") |
slice() |
Extracts a section | arr.slice(1,3) |
splice() |
Adds/removes elements | arr.splice(2, 1, "new") |
Ques: How can you search elements in an array?
Ans: You can search using:
indexOf() → Returns index of first matchlastIndexOf() → Returns index of last matchincludes() → Returns true or falseExample:
let nums = [10, 20, 30, 40];
console.log(nums.includes(20)); // true
Ques: What are functional array methods?
map() → Creates new array from each elementfilter() → Returns elements that pass a testreduce() → Reduces array to a single valueExample:
let nums = [1, 2, 3, 4];
let doubled = nums.map(n => n * 2);
Ques: How do you iterate over arrays?
Ans: There are several ways to loop through an array:
let arr = ["a", "b", "c"];
for (let i = 0; i < arr.length; i++) console.log(arr[i]);
arr.forEach(item => console.log(item));
for (let item of arr) console.log(item);
Ques: How do you sort and reverse arrays?
Ans: Use .sort() for sorting and .reverse() for reversing.
Example:
let numbers = [40, 10, 30, 20];
numbers.sort((a, b) => a - b); // Ascending
numbers.reverse(); // Descending
Ques: What are Array Iteration Methods?
| Method | Purpose |
|---|---|
forEach() |
Executes a function for each element |
map() |
Returns a new array with transformed values |
filter() |
Returns elements that match a condition |
reduce() |
Accumulates values into one result |
some() |
Returns true if any element matches |
every() |
Returns true if all elements match |
find() |
Returns first matching element |
findIndex() |
Returns index of first match |
Ques: What is the difference between map() and forEach()?
| Feature | map() |
forEach() |
|---|---|---|
| Returns new array? | Yes | No |
| Use case | Transform data | Iterate for side-effects |
Example:
let arr = [1, 2, 3];
let doubled = arr.map(x => x * 2);
console.log(doubled); // [2,4,6]
Ques: What is an Array Reference in JavaScript?
Ans: Arrays are reference types, meaning they store a reference (address), not the actual value.
let a = [1, 2, 3];
let b = a;
b.push(4);
console.log(a); // [1,2,3,4] - both point to same reference
Ques: How do you copy an array properly?
Ans: Use spread operator or slice() for shallow copies.
let a = [1, 2, 3];
let b = [...a]; // or a.slice()
Ques: What are Typed Arrays in JavaScript?
Ans: Typed Arrays are special array-like objects that handle binary data efficiently. They are used in performance-heavy tasks like WebGL, audio, and video processing.
Example:
let buffer = new ArrayBuffer(8);
let view = new Uint8Array(buffer);
view[0] = 255;
console.log(view); // Uint8Array(8) [255, 0, 0, 0, 0, 0, 0, 0]
Ques: What are the advantages of using Arrays?
map, filter, etc.)