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
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
Count number of vowels found in a string using ↴
for...of loop → iterates through the values of an iterable object, such as an array, string, or map.
includes() method → returns true if an array contains a specified value, otherwise returns false.
toLowerCase() method → returns the value of the string converted to lower case.
for...of loop iterates through the values of an iterable object, such as an Array, String, Set, Map, ...
syntax
for (variable of iterable) {}
variable holds the current value of the iteration.
of keyword indicates that the loop should iterate over the values of the iterable.
iterable object that is iterable, such as an Array, String, Set, Map, ...
Iterate over each character in the string.
const str3 = "ABC";
for (const char of str3) {
console.log(char);
} returns ↴
A
B
C → printed to console
The loop will run three times, once for each character in the string.
On each iteration, the value of the current element is stored in the variable char
For each iteration of the loop, the current value of char is printed to the console.
toLowerCase() method converts all letters to lower case. The original string is unchanged.
const str4 = "hELlo wORLd";
str4.toLowerCase(); returns ↴
"hello world" → lower case
includes() method determines whether an array includes a certain value among its entries, returning true or false.
const arr2 = [1, 2, 3, 4, 5, 6];
arr2.includes(4); returns boolean ↴
true → 4 found in array
const arr3 = [1, 2, 3, 4, 5, 6];
arr3.includes(7); returns boolean ↴
false → 7 NOT found in array
Initialize a string to count the number of vowels.
const string1 = "HELLO World"; → user input
Define a function countVowels to count number of vowels found in a string.
function countVowels(str) {}
The function takes a string as input, str and returns the number of vowel characters found in that string.
Convert str to lower case.
const lowerStr = str.toLowerCase() lowerStr
This ensures the search will be case in-sensitive and both lower case and upper case vowels will be found.
Initialize an array of vowel characters.
const vowels = ["a", "e", "i", "o", "u"] vowels
Initialize count of vowels to zero.
let count = 0 count
Iterate through each character in lowerStr
for (const char of lowerStr)
If current char is in vowels array.
if (vowels.includes(char))
Increment count by 1
count++
Once the loop has completed return the count.
return count
Call the function with ↴
countVowels(string1);
Count number of vowels found in a string.
const string1 = "HELLO World";
function countVowels(str) {
const vowels = ["a", "e", "i", "o", "u"];
const lowerStr = str.toLowerCase();
let count = 0;
for (const char of lowerStr) {
if (vowels.includes(char)) {
count++;
}
}
return count;
}
call function
countVowels(string1); returns ↴
3 → vowels found "e" "o" "o"
Alternative ↴
Use a string instead of an array.
const vowels = ["a", "e", "i", "o", "u"]; → array
const vowels = "aeiou"; → string