Author: MDBootstrap
Loops can execute a block of code as long as a specified condition is true.
The while
loop loops through a block of code as long as a specified condition is true.
Syntax
while (condition) {
// code block to be executed
}
Example
In the following example, the code in the loop will run, over and over again, as long as a variable (i) is less than 10:
var i = 0;
while (i < 10) {
i++;
console.log(i); // Open the console to see the result
}
Live preview
Warning: If you forget to increase the variable used in the condition, the loop will never end. This will crash your browser.
The Do/While Loop
The do/while
loop is a variant of the while loop. This loop will
execute the code block once, before checking if the condition is true, then it will
repeat the loop as long as the condition is true.
Syntax
do {
// code block to be executed
}
while (condition);
Example
The example below uses a do/while
loop. The loop will always be
executed at least once, even if the condition is false, because the code block
is executed before the condition is tested:
do {
text += "The number is " + i;
i++;
}
while (i < 10);
Do not forget to increase the variable used in the condition, otherwise the loop will never end!
Exercises - test your knowledge
Exercise 1
Create a while
loop that runs as long as i
is less than 10.
var i = 0;
while (i < 10) {
i++;
console.log(i);
}
Exercise 2
Create a loop that runs as long as i
is less than 10,
but increase i
with 2 each time.
var i = 0;
while (i < 10) {
i = i +2;
console.log(i);
}
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