Should You Declare Global Variables Inside Functions in JavaScript?

Declaring Global Variables within Functions: An Exploration

In the realm of JavaScript, the "var" keyword is often used to declare variables. However, it's also possible to declare variables without it. This practice results in the creation of global variables, leading some developers to question its usefulness. This article examines the concept and its potential benefits.

According to w3schools, declaring a variable without "var" within a function makes it globally accessible. While this may seem intriguing, it's important to understand that such declarations do not offer any memory optimization advantages.

The so-called "Horror of Implicit Globals" arises when variables are declared implicitly within functions. For instance, consider the following function:

<code class="javascript">function foo() {
    variable1 = 5;
    variable2 = 6;
    return variable1 + variable2;
}</code>

Due to a typo in the second line ("varaible2"), it creates a global variable with the misspelled name. Consequently, the function returns NaN instead of 11, as one might expect.

Furthermore, it's crucial to note that implicitly declared global variables can easily lead to naming collisions and code conflicts, making it difficult to maintain and debug. For these reasons, it's strongly recommended to avoid declaring global variables within functions. Instead, explicitly declare variables using the "var" keyword to ensure proper variable scope and prevent unintended global pollution.

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