The delete operator should only be used to delete properties from objects. Using it to delete variables makes code hard to maintain and will break in strict mode.

If the variable you are deleting is a global variable, this is a sign that your code relies too much on global state. Try encapsulating this global state by means of one of the module patterns introduced in JavaScript: The Good Parts.

In the following code snippet, delete is used to clean up the global cache variable used by function get.

It would be clearer to wrap the whole module into a closure like this (which also avoids exposing function compute to the outside world):

JSLint Error Explanations: Only properties should be deleted.