What is the significance of using parentheses around a function in JavaScript?

Currently, I am developing an application using Java and JavaScript, and while reviewing some code today, I came across a segment that seemed confusing to me.

 var myVariable = (function(configObj){
    var width = configObj.width;
    var height = configObj.height;
 })

 gadgetFuncArray.push(myVariable);

It appears to be creating an array of functions, but the purpose of pushing configuration options as an array of functions is unclear to me.

What are your thoughts on this?

Answer №1

In this scenario, the parentheses serve no functional purpose and can be easily eliminated. Some individuals occasionally (although less frequently since ES6) use these parentheses to create an Immediately-invoked Function Expression (IIFE). As stated on the Wikipedia page:

Immediately-invoked function expressions can be utilized to prevent variable hoisting within blocks, safeguard against contaminating the global environment, and also allow for public access to methods while maintaining privacy for variables defined within the function.

This concept can be illustrated as follows: (function () {})()

I suggest delving into Kyle Simpson's comprehensive ebook titled You Don't Know JS, specifically focusing on the sections related to scope and closures.

Answer №2

When you wrap a function in parentheses, it doesn't add any special functionality. Typically, this is done for Immediately Invoked Function Expressions (IIFE) when you want to call the function right after declaring it:

var module = (function foo(config) {
   return {
      getConfig: function() {
         return config.my;
      }
   }
}({ my: 'config' }));

However, it doesn't seem like that's what's happening in the code you shared. There are valid reasons for having an array of functions, although it may not be immediately clear from the provided code snippet.

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