Why Are Global Variables Considered Harmful in JavaScript?

Understanding the Pitfalls of Global Variables in JavaScript

Despite the common practice of avoiding global variables in JavaScript, it's often unclear why such caution is advised. While it's true that global variables can clutter up the global namespace, is there anything more to their negative reputation?

The Impact on Performance and Compatibility

Beyond namespace concerns, global variables carry performance implications. Compared to local variables, accessing global variables is time-consuming for JavaScript. While the time difference may be negligible, it exists nonetheless.

Cluttered Namespace and Unexpected Redeclarations

A clutter of global variables can lead to memory leaks and unexpected redeclarations. Declaring a variable as global without proper declaration (e.g., using the "var" keyword) can result in implied globals, exacerbating the issue. When a redeclaration occurs in a different scope, unforeseen consequences can arise.

Experts' Perspective

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