JavaScript
/Beginner
Arrays & Methods
Definition
An ordered, integer-indexed collection of values. JavaScript arrays can hold mixed data types and dynamically resize themselves.
Explain Like I'm New
An array is a list of items kept in a specific order, like a grocery list. Item 0 is milk, Item 1 is bread. You can easily add items to the end (`push`), remove from the end (`pop`), or loop through all of them (`forEach`).
Real World Example
Storing a list of a user's recent transactions, and using `array.reduce()` to calculate the total sum of their expenses.
Common Use Cases
- •Storing ordered data
- •Iterating and transforming lists of objects
Terminal Output
bash / terminal
const numbers = [1, 2, 3, 4, 5];
// Map: Returns a new array (creates [2, 4, 6, 8, 10])
const doubled = numbers.map(num => num * 2);
// Filter: Returns a new array with items that pass the test
const evens = numbers.filter(num => num % 2 === 0);
// Reduce: Condenses the array into a single value
const sum = numbers.reduce((accumulator, currentVal) => accumulator + currentVal, 0);
// Splice: Mutates original array (Removes 1 item at index 2)
numbers.splice(2, 1);
console.log(numbers); // [1, 2, 4, 5]
Interview Questions
basic
- What is the difference between `map` and `forEach`?
intermediate
- What is the difference between `slice` and `splice`?
advanced
- Why is sorting an array of numbers `[1, 10, 2].sort()` dangerous in JS?