Revision 118797 of Values

<div class="note"><strong>Note:</strong> This page is obsolete and has been merged into <a href="/en/Core_JavaScript_1.5_Guide/Core_Language_Features#Values" title="en/Core JavaScript 1.5 Guide/Core Language Features#Values">Core Language Features</a></div>
<h2>Introduction</h2>
<p>JavaScript recognizes the following types of values:</p>
<ul> <li><a href="/en/Core_JavaScript_1.5_Reference/Global_Objects/Number" title="en/Core_JavaScript_1.5_Reference/Global_Objects/Number">Numbers</a>, such as 42 or 3.14159</li> <li><a href="/en/Core_JavaScript_1.5_Reference/Global_Objects/Boolean" title="en/Core_JavaScript_1.5_Reference/Global_Objects/Boolean">Logical (Boolean)</a> values, either <code>true</code> or <code>false</code></li> <li><a href="/en/Core_JavaScript_1.5_Reference/Global_Objects/String" title="en/Core_JavaScript_1.5_Reference/Global_Objects/String">Strings</a>, such as "Howdy!"</li> <li><code>null</code>, a special keyword denoting a null value; <code>null</code> is also a primitive value. Because JavaScript is case-sensitive, <code>null</code> is not the same as <code>Null</code>, <code>NULL</code>, or any other variant</li> <li><code><a href="/en/Core_JavaScript_1.5_Reference/Global_Properties/undefined" title="en/Core_JavaScript_1.5_Reference/Global_Properties/undefined">undefined</a></code>, a top-level property whose value is undefined; <code>undefined</code> is also a primitive value.</li>
</ul>
<p>This relatively small set of types of values, or <em>data types</em>, enables you to perform useful functions with your applications. There is no explicit distinction between integer and real-valued numbers. Nor is there an explicit date data type in JavaScript. However, you can use the <code><a href="/en/Core_JavaScript_1.5_Reference/Global_Objects/Date" title="en/Core_JavaScript_1.5_Reference/Global_Objects/Date">Date</a></code> object and its methods to handle dates. <a href="/en/Core_JavaScript_1.5_Reference/Global_Objects/Object" title="en/Core_JavaScript_1.5_Reference/Global_Objects/Object">Objects</a> and <a href="/en/Core_JavaScript_1.5_Reference/Global_Objects/Function" title="en/Core_JavaScript_1.5_Reference/Global_Objects/Function">functions</a> are the other fundamental elements in the language. You can think of objects as named containers for values, and functions as procedures that your application can perform.</p>
<h2>Data Type Conversion</h2>
<p>JavaScript is a dynamically typed language. That means you do not have to specify the data type of a variable when you declare it, and data types are converted automatically as needed during script execution. So, for example, you could define a variable as follows:</p>
<pre class="brush: js">var answer = 42;
</pre>
<p>And later, you could assign the same variable a string value, for example:</p>
<p> </p>
<pre>answer = "Thanks for all the fish...";
</pre>
<p> </p>
<p>Because JavaScript is dynamically typed, this assignment does not cause an error message.</p>
<p>In expressions involving numeric and string values with the + operator, JavaScript converts numeric values to strings. For example, consider the following statements:</p>
<pre class="eval">x = "The answer is " + 42 // returns "The answer is 42"
y = 42 + " is the answer" // returns "42 is the answer"
</pre>
<p>In statements involving other operators, JavaScript does not convert numeric values to strings. For example:</p>
<pre class="eval">"37" - 7 // returns 30
"37" + 7 // returns "377"
</pre>
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