Summary
Creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement executed in the loop.
Version Information
Statement | |
Implemented in: | JavaScript 1.0, NES 2.0 |
ECMA Version: | ECMA-262 |
Syntax
for ([initialization]; [condition]; [final-expression]) statement
Parameters
-
initialization
-
An expression (including assignment expressions) or variable declaration. Typically used to initialize a counter variable. This expression may optionally declare new variables with the
var
keyword. These variables are not local to the loop, i.e. they are in the same scope thefor
loop is in. The result of this expression is discarded. -
condition
-
An expression to be evaluated before each loop iteration. If this expression evaluates to true,
statement
is executed. This conditional test is optional. If omitted, the condition always evaluates to true. If the expression evaluates to false, execution skips to the first expression following thefor
construct. -
final-expression
-
An expression to be evaluated at the end of each loop iteration. This occurs before the next evaluation of
condition
. Generally used to update or increment the counter variable. -
statement
-
A statement that is executed as long as the condition evaluates to true. To execute multiple statements within the loop, use a block statement (
{ ... }
) to group those statements.
Examples
Example: Using for
The following for
statement starts by declaring the variable i
and initializing it to 0
. It checks that i
is less than nine, performs the two succeeding statements, and increments i
by 1 after each pass through the loop.
for (var i = 0; i < 9; i++) { n += i; myfunc(n); }
Example: Using for
without the statement
section
The following for
cycle calculates the offset position of a node in the [final-expression] section, and therefore it does not require the use of a statement
or block statement
section:
function showOffsetPos (sId) { var nLeft = 0, nTop = 0; for (var oItNode = document.getElementById(sId); oItNode; nLeft += oItNode.offsetLeft, nTop += oItNode.offsetTop, oItNode = oItNode.offsetParent); alert("Offset position of \"" + sId + "\" element:\n left: " + nLeft + "px;\n top: " + nTop + "px;"); }
Note: In this case, when you do not use the
statement
section, a semicolon is put immediately after the declaration of the cycle.