Strings are a sequence of zero or more characters written inside quotes used to represent text.

Strings may consist of letters, numbers, symbols, words, or sentences.

Strings are immutable, they cannot be changed.

Each character in a string has an index.

The first character will be index 0 the second character will be index 1 and so on.

There are two ways to access an individual character in a string.

charAt() method

const str1 = "abc"; string

str1.charAt(0); character at index 0 → "a"

str1.charAt(1); character at index 1 → "b"

str1.charAt(2); character at index 2 → "c"

str1.charAt(3); character at index 3 → "" index not found

Alternatively use at() or slice() methods

bracket notation []

const str2 = "abc"; string

str2[0]; character at index 0 → "a"

str2[1]; character at index 1 → "b"

str2[2]; character at index 2 → "c"

str2[3]; character at index 3 → undefined index not found

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Arrays are used to store multiple values in a single variable.

Each value is called an element, and each element has a numeric position in the array, known as its index.

Arrays are zero-indexed, meaning the first element is at index 0, the second at index 1, and so on.

Arrays can contain any data type, including numbers, strings, and objects.

const arr1 = [2, 4, 6]; array

arr1[0]; element at index 0 → 2

arr1[1]; element at index 1 → 4

arr1[2]; element at index 2 → 6

arr1[3]; element at index 3 → undefined index not found

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Numbers are used to represent both integer and floating-point values.

Numbers are most commonly expressed in literal forms like 255 or 3.14159 ↴

let num1 = 5; → number

let num2 = 2.5; → number

let num3 = num1 + num2;

console.log(num3); returns ↴

7.5 → number

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Alternate case of each character in a string using ↴

for loop → executes a block of code a number of times.

split() method → splits a string into an array of substrings.

join() method → returns an array as a string.

toLowerCase() method → returns the value of the string converted to lower case.

toUpperCase() method → returns the value of the string converted to upper case.

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for loop repeatedly executes a block of code until a specified condition evaluates to false.

The loop runs a block of code a set number of times, defined by an initialization, a condition, and an increment.

for (let x = 0; x < 4; x++) {

console.log(x);

}

Loop variable x is initialized to 0

Condition x < 4 is checked before each iteration.

The loop will continue to run as long as x is less than 4

The loop repeatedly executes a block of code 4 times, from 0 to 3

For each iteration of the loop, the current value of x is printed to the console.

After each iteration, x is incremented by 1 x++

When x reaches 4 the condition evaluates to false, terminating the loop.

0

1

2

3 → printed to console

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split() method splits a string into an array of substrings based on a specified separator. The original string is unchanged.

("") separator → string is split between each character.

(" ") separator → string is split between words.

const str3 = "Hello"; → string

str3.split(""); returns ↴

["H", "e", "l", "l", "o"] → array

const str4 = "hello world"; → string

str4.split(" "); returns ↴

["hello", "world"] → array

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join() method joins all elements of an array into a string based on a specified separator. The original array is unchanged.

("") separator → string is joined with no spaces between each character.

(" ") separator → string is joined with no spaces between each word.

const arr3 = ["Hello", "World"]; array

arr3.join(" "); returns ↴

"Hello World" → string

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toLowerCase() method returns a new string with all letters converted to lower case. The original string is unchanged.

const str5 = "hELlo wORLd";

str5.toLowerCase(); returns ↴

"hello world" → lower case

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toUpperCase() method returns a new string with all letters converted to upper case. The original string is unchanged.

const str6 = "hELlo wORLd";

str6.toUpperCase(); returns ↴

"HELLO WORLD" → upper case

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Initialize a variable to hold the string to alternate case.

const string1 = "hello world"; → user input

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Define a function alternateCase to alternate the case of a string.

function alternateCase(str) {}

The function takes a string as input str and returns a new string with alternating case. The original string remains unchanged.

Convert str to lower case and split it into an array of characters.

let chars = str.toLowerCase().split("") chars → array

Loop through the array, modifying characters at even indices.

Loop increments by 2 to target the even indices x += 2

for (let x = 0; x < chars.length; x += 2) {}

Convert the character at the even index to upper case.

chars[x] = chars[x].toUpperCase()

Join the modified array back into a string and return it.

return chars.join("")

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Call the function with ↴

alternateCase(string1);

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Alternate case of each character in a string.