JavaScript
While Loop
Loops can
execute a block of code as long as a specified condition is true.
The
While Loop
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:
Example
while
(i < 10) {
text += "The number is " + i;
i++;
}
»
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:
Example
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!
Comparing
For and While
If you have
read the previous chapter, about the for loop, you will discover that a while
loop is much the same as a for loop, with statement 1 and statement 3 omitted.
The loop in
this example uses a for loop to collect the car names from the cars array:
Example
var
cars = ["BMW", "Volvo", "Saab",
"Ford"];
var
i = 0;
var
text = "";
for
(;cars[i];) {
text += cars[i] + "<br>";
i++;
}
»
The loop in
this example uses a while loop to collect the car names from the cars array:
Example
var
cars = ["BMW", "Volvo", "Saab",
"Ford"];
var
i = 0;
var
text = "";
while
(cars[i]) {
text += cars[i] + "<br>";
i++;
}
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