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Topics
  1. Understanding Arrays
  2. Understanding Loops
Understanding Arrays
Array Length

The .length property tells you how many elements are in a JavaScript array. 

                                

const numbers = [1, 2, 3, 4];
console.log(numbers.length); // Output: 4
Accessing Array Elements by Index

Array elements are accessed by their index, which starts at 0. Use the array name followed by square brackets with the index inside to get an element. 

                                

const myArray = [100, 200, 300];
console.log(myArray[0]); // Output: 100
console.log(myArray[1]); // Output: 200
console.log(myArray[2]); // Output: 300
Adding Elements with .push()

The .push() method adds one or more elements to the end of an array and returns the new length of the array. 

                                

const cart = ['apple', 'orange'];
cart.push('pear');
console.log(cart); // Output: ['apple', 'orange', 'pear']

const numbers = [1, 2];
numbers.push(3, 4, 5);
console.log(numbers); // Output: [1, 2, 3, 4, 5]
Removing the Last Element with .pop()

The .pop() method removes the last element from an array and returns it. 

                                

const ingredients = ['eggs', 'flour', 'chocolate'];
const poppedIngredient = ingredients.pop();
console.log(poppedIngredient); // Output: 'chocolate'
console.log(ingredients); // Output: ['eggs', 'flour']
Arrays are Mutable

JavaScript arrays are mutable, meaning you can change the contents even if the array is declared with const. 

                                

const names = ['Alice', 'Bob'];
names.push('Carl');
console.log(names); // Output: ['Alice', 'Bob', 'Carl']
Working with Arrays

Arrays can hold different types of data and their contents can be changed using methods like .push() and .pop(). 

                                

const numberArray = [0, 1, 2, 3];
const mixedArray = [1, 'chicken', false];
console.log(numberArray); // Output: [0, 1, 2, 3]
console.log(mixedArray); // Output: [1, 'chicken', false]
Understanding Loops
Looping in Reverse

A for loop can go through an array in reverse by starting with the last index and decreasing the index with each iteration. 

                                

const items = ['apricot', 'banana', 'cherry'];
for (let i = items.length - 1; i >= 0; i--) {
  console.log(`${i}. ${items[i]}`);
}
// Output:
// 2. cherry
// 1. banana
// 0. apricot
Using the Do...While Loop

A do...while loop runs a block of code once before checking if a condition is true. If the condition is true, it repeats the loop. This loop always runs at least once. 

                                

let x = 0;
let i = 0;
do {
  x += i;
  console.log(x);
  i++;
} while (i < 5);
// Output:
// 0
// 1
// 3
// 6
// 10
Using the For Loop

A for loop allows you to repeat a block of code a specific number of times. It uses three parts: the initialization, the condition, and the increment. 

                                

for (let i = 0; i < 4; i++) {
  console.log(i);
}
// Output: 0
// Output: 1
// Output: 2
// Output: 3
Looping Through Arrays

You can loop through each item in an array using its .length property to determine when to stop. 

                                

const array = ['a', 'b', 'c'];
for (let i = 0; i < array.length; i++) {
  console.log(array[i]);
}
// Output:
// 'a'
// 'b'
// 'c'
Exiting a Loop Early with Break

The break keyword lets you exit a loop before it finishes all its iterations, continuing the code after the loop. 

                                

for (let i = 0; i < 99; i++) {
  if (i > 5) {
     break;
  }
  console.log(i);
}
// Output:
// 0
// 1
// 2
// 3
// 4
// 5
Nested Loops

A nested loop is when one loop runs inside another loop. The inner loop will complete all its iterations for each iteration of the outer loop. 

                                

for (let outer = 0; outer < 2; outer++) {
  for (let inner = 0; inner < 3; inner++) {
    console.log(`${outer}-${inner}`);
  }
}
// Output:
// '0-0'
// '0-1'
// '0-2'
// '1-0'
// '1-1'
// '1-2'
Understanding Loops

Loops allow you to repeat a block of code until a certain condition is met. They are essential for automating repetitive tasks. 

                                

let i = 0;
while (i < 5) {
  console.log(i);
  i++;
}
// Output:
// 0
// 1
// 2
// 3
// 4
While Loop

A while loop keeps running as long as its condition is true. It's useful when you don't know how many times you need to repeat the code in advance.

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