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
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
Alternate case of each character in a string using ↴
for loop → executes a block of code a number of times.
modulo operator % (remainder operator) → returns the remainder left over when one operand is divided by a second operand.
toLowerCase() method → returns the value of the string converted to lower case.
toUpperCase() method → returns the value of the string converted to upper case.
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
Modulo operator % (remainder operator) returns the remainder left over when one number is divided by a second number.
10 % 2 → remainder 0
10 % 3 → remainder 1
10 % 4 → remainder 2
10 % 5 → remainder 0
The modulo operator can be used to check whether a number is odd or even.
If a number is divisible by 2 (with no remainder) then it must be an even number.
If a number is not divisible by 2 (with a remainder) then it must be an odd number.
4 % 2 === 0 statement is true, remainder is zero, so 4 is an even number.
5 % 2 === 0 statement is false, remainder is not zero, so 5 is an odd number.
function checkNumber(num) {
if (num % 2 === 0) { if num divisible by 2
console.log(num + " is even"); if true
} else {
console.log(num + " is odd"); if false
}
}
checkNumber(2); → 2 is even
checkNumber(3); → 3 is odd
checkNumber(4); → 4 is even
checkNumber(5); → 5 is odd
toLowerCase() method returns a new string with all letters converted to lower case. The original string is unchanged.
const str3 = "hELlo wORLd";
str3.toLowerCase(); returns ↴
"hello world" → lower case
toUpperCase() method returns a new string with all letters converted to upper case. The original string is unchanged.
const str4 = "hELlo wORLd";
str4.toUpperCase(); returns ↴
"HELLO WORLD" → upper case
Initialize a variable to hold the string to alternate case.
const string1 = "hello world"; → user input
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.
Initialize an empty string to hold the result.
let strAlt = "" strAlt
Loop through each character in str
for (let x = 0; x < str.length; x++) {}
Using the modulo operator, check if the current index x is even.
if (x % 2 === 0)
If true, convert the character to upper case and append to strAlt
strAlt += str[x].toUpperCase()
else if false, convert the character to lower case and append to strAlt
strAlt += str[x].toLowerCase()
Return the formatted string.
return strAlt
Call the function with ↴
alternateCase(string1);
Alternate case of each character in a string.
const string1 = "hello world";
function alternateCase(str) {
let strAlt = "";
for (let x = 0; x < str.length; x++) {
if (x % 2 === 0) {
strAlt += str[x].toUpperCase();
} else {
strAlt += str[x].toLowerCase();
}
}
return strAlt;
}
call function
alternateCase(string1); returns ↴
"HeLlO WoRlD"