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.
Example
See https://gist.github.com/1092039
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.
Filed under: JavaScript, global, global scope, JavaScript, private, private scope, quirk, scope, variables
