JavaScript Loops examples (while, do while, for)

LOOPS/
R E C U R S I O N
J AVA S C R I P T
G R A D E – 1 1

LOOPS
• A loop is a construct that repeats a set number of times, usually
based on a condition
Example :
You may want to output a number ten times. Instead of writing the
same line of code ten times, you can put it in a loop, which reduces
the amount of code.
You may not know how many times some code needs to be run. For
example, you want to multiply a number by itself until it is greater
than 1000.You will not know, at the start, how many times this code
needs to be run.

TYPE OF LOOPS
•For
•DoWhile
•While

DO/WHILE
• In this loop the condition is checked at the end of the loop, which means the loop will always
run at least once:
• Example 1:
var count = 0;
do
{
document.write (count * count);
count++;
}
while (count <=12);
In this example, 0*0 will always be output, the the value of count is checked and it decides
if the loop will run again.

WHILE
• A while loop runs the code while a condition.
• Example 1:
var count = 0;
while (count <=12)
{
document.write(count *count);
count++;
}
This loop will display 12 square numbers.
• Example 2:
var check = true;
while (check = true)
{
document.write(“It’s true”);
}
At the moment this loop will run infinitely.While
the variable check is true, it will continue to run.

FOR
• In a for loop, you need to know the number of times the loop is to run.
• Example 1 :
The code below adds the value of total to itself ten times :
for (count = 0; count < 10; count++)
{
total = count;
document.write (total);
}
• Example 2 :
The for loop shown below will write the first 12 square numbers :
for (count = 1; count <=12; count++)
{
document.write(count*count);
}

JavaScript Loops examples (while, do while, for)

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