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copied!<p><strong>strong/weak</strong> <em>can</em> be thought of in relation to how the compiler, if applicable, handles typing.</p> <ul> <li><p><a href="http://en.wikipedia.org/wiki/Programming_language#Weak_and_strong_typing" rel="noreferrer"><strong>Weakly typed</strong></a> means the compiler, if applicable, doesn't enforce correct typing. Without implicit compiler interjection, the instruction will error during run-time.</p> <pre><code>"12345" * 1 === 12345 // string * number => number </code></pre> <p><strong><em>Strongly typed</em></strong> means there is a compiler, and it wants you an explicit cast from <em>string</em> to <em>integer</em>.</p> <pre><code>(int) "12345" * 1 === 12345 </code></pre> <p>In either case, some compiler's features can implicitly alter the instruction during compile-time to do conversions for you, if it can determine that is the right thing to do.</p> <p>Thus far, JavaScript can be categorized as Not-Strongly-Typed. That either means it's weakly-typed or un-typed.</p></li> </ul> <p><strong>dynamic/static</strong> <em>can</em> be thought of in relation to how the language instructions manipulate types.</p> <ul> <li><p><a href="http://en.wikipedia.org/wiki/Programming_language#Static_versus_dynamic_typing" rel="noreferrer"><strong>Dynamically typed</strong></a> means the <strong>value</strong>'s type is enforced, but the variable simply represents any value of any type.</p> <pre><code>x = 12345; // number x = "string"; // string x = { key: "value" }; // object y = 123 + x; // error or implicit conversion must take place. </code></pre> <p><strong><em>Statically typed</em></strong> means the <strong>variable</strong> type is strongly enforced, and the value type is less-so enforced.</p> <pre><code>int x = 12345; // binds x to the type int x = "string"; // too late, x is an integer - error string y = 123; // error or implicit conversion must take place. </code></pre> <p>Thus far, JavaScript can be categorized as Not-Statically-Typed. Also, it appears to be Dynamically Typed, if typed at all. So we need to see what Typing means.</p></li> </ul> <p><a href="http://en.wikipedia.org/wiki/Programming_language#Typed_versus_untyped_languages" rel="noreferrer"><strong>Typed</strong></a> means that the language distinguishes between different types such as <em>string</em>, <em>number</em>, <em>boolean</em>, <em>object</em>, <em>array</em>, <em>null</em>, <em>undefined</em> and so on. Also each operation is bound to specific types. So you cannot divide an <em>integer</em> by a <em>string</em>.</p> <pre><code> 2 / "blah" // produces NaN </code></pre> <p><strong><em>Untyped</em></strong> means the operation of dividing <em>integer</em> by <em>string</em> would result in treating the first four bytes of <em>string</em> as <em>integer</em>. This is because Untyped operations take place directly on bits, there are no types to observe. The outcome will be something quite unexpected:</p> <pre><code> 2 / "blah" // will be treated as 2 / 1500275048 </code></pre> <p>Since JavaScript behaves according to the definition of being Typed, it must be. And therefore it must be Dynamically Typed, and Weakly Typed.</p> <p>If anybody claims JavaScript is Untyped, it is merely for academic theory, not for practical application.</p>

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