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copied!<p>Drop the semicolon after the function definition.</p> <pre><code>(function (msg){alert(msg)}) ('SO'); </code></pre> <p>Above should work.</p> <p>DEMO Page: <a href="https://jsfiddle.net/e7ooeq6m/" rel="noreferrer">https://jsfiddle.net/e7ooeq6m/</a></p> <p>I have discussed this kind of pattern in this post:</p> <p><a href="https://stackoverflow.com/questions/1122690/jquery-and-questions/1122740#1122740">jQuery and $ questions</a></p> <p><strong>EDIT:</strong></p> <p>If you look at <a href="http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf" rel="noreferrer">ECMA script specification</a>, there are 3 ways you can define a function. (Page 98, Section 13 Function Definition)</p> <h2>1. Using Function constructor</h2> <pre><code>var sum = new Function('a','b', 'return a + b;'); alert(sum(10, 20)); //alerts 30 </code></pre> <h2>2. Using Function declaration.</h2> <pre><code>function sum(a, b) { return a + b; } alert(sum(10, 10)); //Alerts 20; </code></pre> <h2>3. Function Expression</h2> <pre><code>var sum = function(a, b) { return a + b; } alert(sum(5, 5)); // alerts 10 </code></pre> <p>So you may ask, what's the difference between declaration and expression? </p> <p>From ECMA Script specification:</p> <blockquote> <p>FunctionDeclaration : function Identifier ( FormalParameterListopt ){ FunctionBody }</p> <p>FunctionExpression : function Identifieropt ( FormalParameterListopt ){ FunctionBody }</p> </blockquote> <p>If you notice, 'identifier' is <strong>optional</strong> for function expression. And when you don't give an identifier, you create an anonymous function. It doesn't mean that you can't specify an identifier.</p> <p>This means following is valid.</p> <pre><code>var sum = function mySum(a, b) { return a + b; } </code></pre> <p>Important point to note is that you can use 'mySum' only inside the mySum function body, not outside. See following example:</p> <pre><code>var test1 = function test2() { alert(typeof test2); } alert(typeof(test2)); //alerts 'undefined', surprise! test1(); //alerts 'function' because test2 is a function. </code></pre> <p><a href="http://jsbin.com/esupa" rel="noreferrer">Live Demo</a></p> <p>Compare this to</p> <pre><code> function test1() { alert(typeof test1) }; alert(typeof test1); //alerts 'function' test1(); //alerts 'function' </code></pre> <hr> <p>Armed with this knowledge, let's try to analyze your code.</p> <p>When you have code like, </p> <pre><code> function(msg) { alert(msg); } </code></pre> <p>You created a function expression. And you can execute this function expression by wrapping it inside parenthesis.</p> <pre><code> (function(msg) { alert(msg); })('SO'); //alerts SO. </code></pre>

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