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Loops in JavaScript

Loops in JavaScript

JavaScript loops

Loops are used to repetitively run a piece of code over and over again without necessarily writing it repeatedly

Loops can execute a certain block of code a number of times.

In programming loops are used to repeat a block of code.

Loops are useful in programming for example when fetching an array of elements from the database

There are five types JavaScript loops

  • for loop
  • while loop
  • do-while loop
  • for-in loop
  • for-of loop

For loop

The for loops runs over a code of a fixed number of times with a known number of iterations

The syntax is

for(initializer;condition;iterator){
//code
}
  • initializer – executes once once the loop begins
  • condition – checked before every loop if false loop terminates
  • iterator – execute after the body on each iteration

Example a program to print number one to nine using for loop

for(i=0;i<10;i++){
console.log(i)
}

while loop

While loop iterates the elements for infinite number of times and the number of iterations is not known

syntax

while(){
//code
}

Example program to print numbers one to nine using while loop

i = 1
while(i<10){
console.log(i)
i++
}

do .. while loop

It repeats a itself a number of times in a block code just like the while loop, the code is executed at least once whether the condition is true or false

syntax

do{
//code body

} while()

Example program to display numbers one to nine using do.. while loop

i = 0

do{
i++
console.log(i)

} while(i<9)

for in loop

This loop allows you to repetitively run a code over all property keys of an object

Syntax

for(key in object){
// code body
}

Example a program to print numbers one to nine using for in loop

const number = [1,2,3,4,5,6,7,8,9]

for(i in number){
console.log(number[i])
}

for… of loop

The for .. of loop allows you to repetitively run a block of code over iterable objects

The syntax

for(element of iterable){
// code body
}

Example program to print numbers one to nine using for… of loop

const number = [1,2,3,4,5,6,7,8,9]

for(i of number){
console.log(i)
}

You can also learn about JavaScript array methods here