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
Case sensitivity defines whether uppercase and lowercase letters are treated as distinct or equivalent.
case-sensitive will distinguish between uppercase and lowercase letters.
"A" will be treated as distinct to the letter "a" and vice versa. They will be treated as different.
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 occurrences of a character in a string using the split() method.
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
length property returns the number of characters in a string.
const str5 = "Hello World";
str5.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 str6 = "Hello World";
str6.length - 1; returns ↴
10 → end index of string
Initialize a variable to hold the string to be searched.
const string1 = "HELLO WORLD, hello world"; → user input
Initialize a variable to hold the character to count.
const char1 = "o"; → user input
Define a function countOccurrences to count occurrences of a character in a string.
function countOccurrences(str, char) {}
The function takes two parameters ↴
string1 the string to be searched, str
char1 the character to count, char
The function returns the number of occurrences of the specified character found in the string.
split() method splits a string into an array of substrings based on a specified separator.
The character that we want to count is used as the separator.
const str = "Hello World" string to search
const char = "o" "o" separator
str.split(char) returns ↴
['Hell', ' W', 'rld'] array with 3 substrings
The string will be split wherever it finds the character "o"
And will remove the separator character "o" from the string.
length property of an Array instance represents the number of elements in that array.
The number of occurrences of the character is one less than the number of substrings.
Subtract 1 from the length to get the final count and return.
return str.split(char).length - 1
Call the function with ↴
countOccurrences(string1, char1);
Count occurrences of the character "o" in a string | case-sensitive
const string1 = "HELLO WORLD, hello world";
const char1 = "o";
function countOccurrences(str, char) {
return str.split(char).length - 1;
}
call function
countOccurrences(string1, char1); returns ↴
2
Alternative using an arrow function ↴
const countOccurrences2 = (str, char) => str.split(char).length - 1;
countOccurrences2(string1, char1);