while (boolean expr)
statement
or
do
statement
while (boolean expr);
Example:
var j = 0;
while (j < 10)
{
alert (j + " " + j * j);
j++;
}
for ( init ; test ; incr )
statement
init
and incr
usually involve assignments. Both can be comma-separated lists of statements.
init
sets initial conditions.
test
is a boolean condition: the loop executes as long as it is true
.
incr
is executed after statement, every time round the loop.
init
and incr
are optional but there must always be the two semicolons to mark the sections of the loop header.
Example:
for (var i = 0, j = 10; i < j; i++, j--)
{
if (3 * i > 2 * j)
alert (i + " " + j);
}
When writing loops it is important to identify repetitive computations that can be done before the loop rather than every time round it. This is possibly the most important factor to look out for, to make your code run faster.
There is another kind of loop in JavaScript but it can only be introduced after we have covered Objects.