Function Overloading concept in Javascript Most object-oriented - TopicsExpress

Function Overloading concept in Javascript Most object-oriented languages support function overloading, which is the ability of a single function to have multiple signatures. A function signature is made up of the function name plus the number and type of parameters the function expects. Thus, a single function can have one signature that accepts a single string argument and another that accepts two numeric arguments. The language determines which version of a function to call based on the arguments that are passed in. As mentioned previously, JavaScript functions can accept any number of parameters, and the types of parameters a function takes aren’t specified at all. That means JavaScript functions don’t actually have signatures. A lack of function signatures also means a lack of function overloading. Look at what happens when you try to declare two functions with the same name: function sayMessage(message) { console.log(message); } function sayMessage() { console.log(Default message); } sayMessage(Hello!); // outputs Default message If this were another language, the output of sayMessage(Hello!) would likely be Hello!. In JavaScript, however, when you define multiple functions with the same name, the one that appears last in your code wins. The earlier function declarations are completely removed, and the last is the one that is used. Once again, it helps to think about this situation The fact that functions don’t have signatures in JavaScript doesn’t mean you can’t mimic function overloading. You can retrieve the number of parameters that were passed in by using the arguments object, and you can use that information to determine what to do. For example: function sayMessage(message) { if (arguments.length === 0) { message = Default message; } console.log(message); } sayMessage(Hello!); // outputs Hello! In this example, the sayMessage() function behaves differently based on the number of parameters that were passed in. If no parameters are passed in (arguments.length === 0), then a default message is used. Otherwise, the first parameter is used as the message. This is a little more involved than function overloading in other languages, but the end result is the same. If you really want to check for different data types, you can use typeof and instanceof. NOTE In practice, checking the named parameter against undefined is more common than relying on arguments.length. The Principle of object-Oriented javascript -- Nicholas C. Zakas

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