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
Check if number is prime using ↴
for loop → executes a block of code a number of times.
Math.sqrt() static method → returns the square root of number.
modulo operator % (remainder operator) → returns the remainder left over when one operand is divided by a second operand.
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
Math.sqrt() static method → returns the square root of number.
const num4 = 81;
Math.sqrt(num4); returns ↴
9
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
10 % 6 → remainder 4
10 % 7 → remainder 3
10 % 8 → remainder 2
10 % 9 → remainder 1
10 % 10 → remainder 0
10 % 2 === 0 → 10 is divisible by 2
10 % 5 === 0 → 10 is divisible by 5
10 % 10 === 0 → 10 is divisible by 10
Initialize a variable to hold the number to check if it is prime.
const number1 = 17; → user input
Define a function isPrime to check if number is prime.
function isPrime(num) {}
The function takes a number as input num and returns true if number is prime, otherwise it returns false.
The function iterates up to the square root of the number, which reduces the number of checks needed.
If num is less than or equal to 1, it is not prime.
if (num <= 1) return false
If true, return false and end execution of function.
If num greater than 1, loop through all numbers from 2 to Math.sqrt(num)
This reduces the number of checks needed.
for (let x = 2; x <= Math.sqrt(num); x++) {}
For each iteration, use the modulo operator to check if num is divisible by x
if (num % x === 0) return false
If true, it is not prime.
If it finds any divisor, return false and end execution of function.
If the loop completes without finding any divisors, num is a prime number. Return true.
return true
If the function returns true, the number is a prime number ✔
If the function returns false, the number is not a prime number ✖
Call the function with ↴
isPrime(number1);
Check if number is prime.
const number1 = 17;
function isPrime(num) {
if (num <= 1) return false;
for (let x = 2; x <= Math.sqrt(num); x++) {
if (num % x === 0) return false;
}
return true;
}
call function
isPrime(number1); returns ↴
true
Number 17 is a prime number, function will iterate from 2 to Math.sqrt(17) → 3 times.