codeql/javascript/ql/src/LanguageFeatures/DeleteVar.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>
<overview>
<p>
The <code>delete</code> 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.
</p>

</overview>
<recommendation>

<p>
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 <i>JavaScript: The Good Parts</i>.
</p>

</recommendation>
<example>

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

<sample src="examples/DeleteVar.js" />

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

<sample src="examples/DeleteVarGood.js" />

</example>
</qhelp>