Revision 567109 of if...else

<h2 id="Summary" name="Summary">Summary</h2>
<p>Executes a statement if a specified condition is true. If the condition is false, another statement can be executed.</p>
<h2 id="Version_Information">Version Information</h2>
<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="eval">
if (<em>condition</em>)
   <em>statement1</em>
[else
   <em>statement2</em>]
</pre>
<h2 id="Parameters" name="Parameters">Parameters</h2>
<dl>
 <dt>
  <code>condition</code></dt>
 <dd>
  An expression that evaluates to true or false.</dd>
</dl>
<dl>
 <dt>
  <code>statement1</code></dt>
 <dd>
  Statement that is executed if <code>condition</code> evaluates to true. Can be any statement, including further nested <code>if</code> statements. To execute multiple statements, use a <a href="/en-US/docs/Web/JavaScript/Reference/Statements/block" title="en/JavaScript/Reference/Statements/block">block</a> statement ({ ... }) to group those statements.</dd>
</dl>
<dl>
 <dt>
  <code>statement2</code></dt>
 <dd>
  Statement that is executed if <code>condition</code> evaluates to false and the <code>else</code> clause exists. Can be any statement, including block statements and further nested <code>if</code> statements.</dd>
</dl>
<h2 id="Description" name="Description">Description</h2>
<p>Multiple <code>if...else</code> statements can be nested to create an <code>else if</code> clause:</p>
<pre class="eval">
if (<em>condition1</em>)
   <em>statement1</em>
else if (<em>condition2</em>)
   <em>statement2</em>
else if (<em>condition3</em>)
   <em>statement3</em>
...
else
   <em>statementN</em>
</pre>
<p>To see how this works, this is how it would look like if the nesting were properly indented:</p>
<pre class="eval">
if (<em>condition1</em>)
   <em>statement1</em>
else
   if (<em>condition2</em>)
      <em>statement2</em>
   else
      if (<em>condition3</em>)
...
</pre>
<p>To execute multiple statements within a clause, use a block statement (<code>{ ... }</code>) to group those statements. In general, it is a good practice to always use block statements, especially in code involving nested <code>if</code> statements:</p>
<pre class="eval">
if (<em>condition</em>) {
   <em>statements1</em>
} else {
   <em>statements2</em>
}
</pre>
<p>Do not confuse the primitive boolean values <code>true</code> and <code>false</code> with the true and false values of the <a href="/en/JavaScript/Reference/Global_Objects/Boolean" title="en/JavaScript/Reference/Global_Objects/Boolean">Boolean</a> object. Any value that is not <code>undefined</code>, <code>null</code>, <code>0</code>, <code>NaN</code>, or the empty string (<code>""</code>), and any object, including a Boolean object whose value is false, evaluates to true when passed to a conditional statement. For example:</p>
<pre class="brush: js">
var b = new Boolean(false);
if (b) // this condition evaluates to true
</pre>
<h2 id="Examples" name="Examples">Examples</h2>
<h3 id="Example:_Using_if...else" name="Example:_Using_if...else">Example: Using <code>if...else</code></h3>
<pre class="brush: js">
if (cipher_char === from_char) {
   result = result + to_char;
   x++;
} else {
   result = result + clear_char;
}
</pre>
<h3 id="Example:_Assignment_within_the_conditional_expression" name="Example:_Assignment_within_the_conditional_expression">Example: Assignment within the conditional expression</h3>
<p>It is advisable to not use simple assignments in a conditional expression, because the assignment can be confused with equality when glancing over the code. For example, do not use the following code:</p>
<pre class="brush: js">
if (x = y) {
   /* do the right thing */
}
</pre>
<p>If you need to use an assignment in a conditional expression, a common practice is to put additional parentheses around the assignment. For example:</p>
<pre class="brush: js">
if ((x = y)) {
   /* do the right thing */
}
</pre>