Revision 417091 of for

<h2 id="Summary" name="Summary">Summary</h2>
<p>Creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement executed in the loop.</p>
<h2 id="Version_Information">Version Information</h2>
<table class="standard-table">
  <tbody>
    <tr>
      <td class="header" colspan="2">Statement</td>
    </tr>
    <tr>
      <td>Implemented in:</td>
      <td>JavaScript 1.0, NES 2.0</td>
    </tr>
    <tr>
      <td>ECMA Version:</td>
      <td>ECMA-262</td>
    </tr>
  </tbody>
</table>
<h2 id="Syntax" name="Syntax">Syntax</h2>
<pre class="syntaxbox">
for ([<em>initialization</em>]; [<em>condition</em>]; [<em>final-expression</em>])
   <em>statement</em>
</pre>
<h3 id="Parameters" name="Parameters">Parameters</h3>
<dl>
  <dt>
    <code>initialization</code></dt>
  <dd>
    An expression (including assignment expressions) or variable declaration. Typically used to initialize a counter variable. This expression may optionally declare new variables with the <code>var</code> keyword. These variables are not local to the loop, i.e. they are in the same scope the <code>for</code> loop is in. The result of this expression is discarded.</dd>
  <dt>
    <code>condition</code></dt>
  <dd>
    An expression to be evaluated before each loop iteration. If this expression evaluates to true, <code>statement</code> 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 the <code>for</code> construct.</dd>
  <dt>
    <code>final-expression</code></dt>
  <dd>
    An expression to be evaluated at the end of each loop iteration. This occurs before the next evaluation of <code>condition</code>. Generally used to update or increment the counter variable.</dd>
  <dt>
    <code>statement</code></dt>
  <dd>
    A statement that is executed as long as the condition evaluates to true. To execute multiple statements within the loop, use a <a href="/en-US/docs/JavaScript/Reference/Statements/block" title="JavaScript/Reference/Statements/block">block</a> statement (<code>{ ... }</code>) to group those statements.</dd>
</dl>
<h2 id="Examples" name="Examples">Examples</h2>
<h3 id="Example.3A_Using_for" name="Example.3A_Using_for">Example: Using <code>for</code></h3>
<p>The following <code>for</code> statement starts by declaring the variable <code>i</code> and initializing it to <code>0</code>. It checks that <code>i</code> is less than nine, performs the two succeeding statements, and increments <code>i</code> by 1 after each pass through the loop.</p>
<pre class="brush: js">
for (var i = 0; i &lt; 9; i++) {
   n += i;
   myfunc(n);
}
</pre>
<h3 id="Example.3A_Using_for_without_the_statement_section" name="Example.3A_Using_for_without_the_statement_section">Example: Using <code>for</code> without the <code>statement</code> section</h3>
<p>The following <code>for</code> cycle calculates the offset position of a node in the <em>[final-expression]</em> section, and therefore it does not require the use of a <code>statement</code> or <code><a href="/en-US/docs/JavaScript/Reference/Statements/block" title="JavaScript/Reference/Statements/block">block</a> statement</code> section:</p>
<pre class="brush: js">
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;");
}</pre>
<div class="note">
  <strong>Note:</strong> In this case, when you do not use the <code>statement</code> section, <strong>a semicolon is put immediately after the declaration of the cycle</strong>.</div>
<h2 id="See_also" name="See_also">See also</h2>
<ul>
  <li><a href="/en-US/docs/JavaScript/Reference/Statements/break" title="JavaScript/Reference/Statements/break">break</a></li>
  <li><a href="/en-US/docs/JavaScript/Reference/Statements/continue">continue</a></li>
  <li><a href="/en-US/docs/JavaScript/Reference/Statements/while" title="JavaScript/Reference/Statements/while">while</a></li>
  <li><a href="/en-US/docs/JavaScript/Reference/Statements/do...while" title="JavaScript/Reference/Statements/do...while">do...while</a></li>
  <li><a href="/en-US/docs/JavaScript/Reference/Statements/for...in" title="JavaScript/Reference/Statements/for...in">for...in</a></li>
  <li><a href="/en-US/docs/JavaScript/Reference/Statements/for...of" title="JavaScript/Reference/Statements/for...of">for...of</a></li>
</ul>