Bitesize Bugs

Accidental Global Variables in JavaScript

Omitting the “var” keyword when declaring a variable in JavaScript will scope it to the global namespace.

Thus, the variable is no longer bound to the scope of the parent function or object instance, but accessibile to every other script through the global “window” object.



Avoid accidentally creating global variables by always declaring them with ‘var’.

This problem gets especially frustrating when expecting variables to be private, bound to instances of an object. You soon realize that your instances’ internal states change unexpectedly.







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Bitesize Bugs is a collection of short articles that expose pesky bugs in front-end web technologies like JavaScript, CSS, HTML and browser behaviors gone bad.