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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Check if a string is a palindrome using ↴

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

Regular Expression → patterns used to match character combinations in strings.

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

replace() method → returns a new string with the value(s) replaced.

length property → return the length of a string.

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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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Regular expressions are patterns used to match character combinations in strings.

The Regular Expression /[^A-Za-z0-9]/g defines a regular expression that matches any character that is NOT an upper case or lower case letter or a digit.

^ caret symbol at the beginning of the square brackets, negates the character set.

[^A-Z] matches anything that is NOT enclosed between A and Z

[^a-z] matches anything that is NOT enclosed between a and z

[^0-9] matches anything that is NOT enclosed between 0 and 9

/g flag indicates that the search should be global, meaning it will find all occurrences.

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replace() method searches a string for a value or a regular expression and returns a new string with the value replaced.

If pattern is a string, only the first occurrence will be replaced.

syntax

string.replace(pattern, replacement)

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toLowerCase() method converts all letters to lower case. The original string is unchanged.

const str5 = "hELlo wORLd";

str5.toLowerCase(); returns ↴

"hello world" → lower case

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Combining a regular expression with the toLowerCase() and replace() methods ↴

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length property returns the number of characters in a string.

const str7 = "Hello World";

str7.length; returns ↴

11 → there are 11 characters in the string

Strings are zero indexed, the first character will be index 0

The last character will be at index length -1

To find the last index in a string.

const str8 = "Hello World";

str8.length - 1; returns ↴

10 → end index of string

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Initialize a variable to hold the string to check for a Palindrome.

const string1 = "Kayak"; → user input

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Define a function palindrome to check if a string is a Palindrome.

function palindrome(str) {}

The function takes a string as input str and returns true if the given string is a palindrome, otherwise returns false.

Strings are zero indexed, so last index will be length - 1

Get the end index of cleanedStr for comparison.

Loop through the first half of cleanedStr strLength / 2 (rounded up if odd number)

for (let x = 0; x < strLength / 2; x++) {}

cleanedStr is compared character by character from both ends.

if (cleanedStr[x] !== cleanedStr[endIndex - x])

If characters do not match, return false.

return false function terminates

If all characters match, return true.

return true

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Call the function with ↴

palindrome(string1);

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Check if string is a palindrome

String to be tested: "kayak"

Loop through the first half of the string.

Compare string, character by character, from both ends.

String to be tested: "kayok"

Loop through the first half of the string.

Compare string, character by character, from both ends.

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Check if string is a palindrome.

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Alternative regular expression pattern ↴

/[^A-Za-z0-9]/g same as ↴

/[^a-z0-9]/gi case-insensitive

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Alternative without using variables ↴

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Valid Palindromes ↴

A man, a plan, a canal. Panama

Never odd or even

Pull up if I pull up

Stressed desserts

Evil, olive!

Race car

Radar

Kayak