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
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
Reverse a string using ↴
for loop → executes a block of code a number of times.
split() method → splits a string into an array of substrings.
trim() method → removes whitespace from both ends of the string and returns a new string, without modifying the original string.
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
split() method splits a string into an array of substrings based on a specified separator (delimiter). The original string is unchanged.
("") separator → string is split between each character.
(" ") separator → string is split at each space character, resulting in an array of 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
trim() method removes whitespace from both ends of a string and returns a new string, without modifying the original string.
const str5 = " Hello World "; → string with leading and trailing whitespace
str5.trim(); returns ↴
"Hello World" → string without whitespace
Initialize a variable to hold the string to be reversed.
const string1 = "Cry over spilled milk"; → user input
Define a function reverseWords to reverse a string of words.
function reverseWords(str) {}
The function takes a string as input str and returns a new string with the words in reverse order.
Split the string into an array of words based on spaces.
const wordsArray = str.split(" ") wordsArray
Initialize an empty string to hold the reversed words.
let reversedString = "" reversedString
Loop through the words array in reverse order.
for (let x = wordsArray.length - 1; x >= 0; x--) {}
Append each word followed by a space to the reversedString.
reversedString += wordsArray[x] + " "
Return the reversed string, trimmed of extra spaces.
return reversedString.trim()
Reverse order of words.
str = "Cry over spilled milk"
Loop through the words in reverse order.
Iteration ↴
0 milk
1 milk spilled
2 milk spilled over
3 milk spilled over Cry
Call the function with ↴
reverseWords(string1);
Reverse order of words.
const string1 = "Cry over spilled milk";
function reverseWords(str) {
const wordsArray = str.split(" ");
let reversedString = "";
for (let x = wordsArray.length - 1; x >= 0; x--) {
reversedString += wordsArray[x] + " ";
}
return reversedString.trim();
}
call function
reverseWords(string1); returns ↴
"milk spilled over Cry"
Alternative to remove one or more spaces from string using a regular expression as the separator to split the string into an array of words.
const wordsArray = str.split(/\s+/);