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A Deep Dive into JavaScript Functions
Based on my readership I have to assume most of you are familiar with JavaScript already. Therefore, it may seem odd to include a post on functions. After all, they are one of the most rudimentary components of JavaScript. My assertion is this, just as a person can speak a language without the ability to read or write it, so too can developers use functions in JavaScript and yet be blissfully unaware of their complexities.
Typically developers only become aware of the specifics of functions when something they wrote explodes in their face. My goal in this section is to expose the intricacies of JavaScript functions to you, which will hopefully save you from having to pull syntactic shrapnel from your codebase.
A word of caution before we begin; JavaScript is only as good as its interpreter. While the concepts we’ll consider are well-covered in the language spec, it does not mean that all runtime environments will work the same way. In other words your milage may vary. This section will discuss common misconceptions of JavaScript functions, and the silent bugs they introduce. However, debugging functions in detail is not covered. Fortunately, debugging has been documented by others in the JavaScript community especially in Juriy Zaytsev’s excellent article "Named Function Expressions Demystified".
Blocks in JavaScript
Before we can understand functions in JavaScript we have to understand blocks. JavaScript blocks are nothing more than statements grouped together. Blocks start with a left curly bracket "{" and end with a right one "}". Simply put, blocks allow statements inside the brackets to be executed together. Blocks form the most basic control structure in JavaScript.
Function Arguments
Functions like control flow statements (if, for, while etc.) can be initialized by passing arguments into the function body. In JavaScript variables are either a complex type (e.g. Object, Array) or a primitive type (e.g. String, Integer). When a complex object is supplied as an argument it is passed by reference to the function body. Instead of sending a copy of the variable, JavaScript sends a pointer to its location in memory. Conversely, when passing a primitive type to a function JavaScript passes by value. This difference can lead to subtle bugs because conceptually we often treat functions as a black box, and assume they can only effect the enclosing scope by returning a variable. With pass by reference, the argument object is modified even though it may not returned by the function.
I hope my answer will help you...
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